diff --git a/src/Common/examples/CMakeLists.txt b/src/Common/examples/CMakeLists.txt
index 69580d4ad0e..8383e80d09d 100644
--- a/src/Common/examples/CMakeLists.txt
+++ b/src/Common/examples/CMakeLists.txt
@@ -92,3 +92,8 @@ endif()
 
 clickhouse_add_executable (check_pointer_valid check_pointer_valid.cpp)
 target_link_libraries (check_pointer_valid PRIVATE clickhouse_common_io clickhouse_common_config)
+
+if (TARGET ch_contrib::icu)
+    clickhouse_add_executable (utf8_upper_lower utf8_upper_lower.cpp)
+    target_link_libraries (utf8_upper_lower PRIVATE ch_contrib::icu)
+endif ()
diff --git a/src/Common/examples/utf8_upper_lower.cpp b/src/Common/examples/utf8_upper_lower.cpp
new file mode 100644
index 00000000000..826e1763105
--- /dev/null
+++ b/src/Common/examples/utf8_upper_lower.cpp
@@ -0,0 +1,27 @@
+#include <iostream>
+#include <unicode/unistr.h>
+
+std::string utf8_to_lower(const std::string & input)
+{
+    icu::UnicodeString unicodeInput(input.c_str(), "UTF-8");
+    unicodeInput.toLower();
+    std::string output;
+    unicodeInput.toUTF8String(output);
+    return output;
+}
+
+std::string utf8_to_upper(const std::string & input)
+{
+    icu::UnicodeString unicodeInput(input.c_str(), "UTF-8");
+    unicodeInput.toUpper();
+    std::string output;
+    unicodeInput.toUTF8String(output);
+    return output;
+}
+
+int main()
+{
+    std::string input = "ır";
+    std::cout << "upper:" << utf8_to_upper(input) << std::endl;
+    return 0;
+}
diff --git a/src/Functions/LowerUpperImpl.h b/src/Functions/LowerUpperImpl.h
index d463ef96e16..a52703d10c8 100644
--- a/src/Functions/LowerUpperImpl.h
+++ b/src/Functions/LowerUpperImpl.h
@@ -1,7 +1,6 @@
 #pragma once
 #include <Columns/ColumnString.h>
 
-
 namespace DB
 {
 
diff --git a/src/Functions/LowerUpperUTF8Impl.h b/src/Functions/LowerUpperUTF8Impl.h
index eedabca5b22..5da085f48e5 100644
--- a/src/Functions/LowerUpperUTF8Impl.h
+++ b/src/Functions/LowerUpperUTF8Impl.h
@@ -1,15 +1,14 @@
 #pragma once
+
+#include "config.h"
+
+#if USE_ICU
+
 #include <Columns/ColumnString.h>
 #include <Functions/LowerUpperImpl.h>
-#include <base/defines.h>
-#include <Poco/UTF8Encoding.h>
+#include <base/find_symbols.h>
+#include <unicode/unistr.h>
 #include <Common/StringUtils.h>
-#include <Common/UTF8Helpers.h>
-
-#ifdef __SSE2__
-#include <emmintrin.h>
-#endif
-
 
 namespace DB
 {
@@ -19,71 +18,7 @@ namespace ErrorCodes
     extern const int BAD_ARGUMENTS;
 }
 
-/// xor or do nothing
-template <bool>
-UInt8 xor_or_identity(const UInt8 c, const int mask)
-{
-    return c ^ mask;
-}
-
-template <>
-inline UInt8 xor_or_identity<false>(const UInt8 c, const int)
-{
-    return c;
-}
-
-/// It is caller's responsibility to ensure the presence of a valid cyrillic sequence in array
-template <bool to_lower>
-inline void UTF8CyrillicToCase(const UInt8 *& src, UInt8 *& dst)
-{
-    if (src[0] == 0xD0u && (src[1] >= 0x80u && src[1] <= 0x8Fu))
-    {
-        /// ЀЁЂЃЄЅІЇЈЉЊЋЌЍЎЏ
-        *dst++ = xor_or_identity<to_lower>(*src++, 0x1);
-        *dst++ = xor_or_identity<to_lower>(*src++, 0x10);
-    }
-    else if (src[0] == 0xD1u && (src[1] >= 0x90u && src[1] <= 0x9Fu))
-    {
-        /// ѐёђѓєѕіїјљњћќѝўџ
-        *dst++ = xor_or_identity<!to_lower>(*src++, 0x1);
-        *dst++ = xor_or_identity<!to_lower>(*src++, 0x10);
-    }
-    else if (src[0] == 0xD0u && (src[1] >= 0x90u && src[1] <= 0x9Fu))
-    {
-        /// А-П
-        *dst++ = *src++;
-        *dst++ = xor_or_identity<to_lower>(*src++, 0x20);
-    }
-    else if (src[0] == 0xD0u && (src[1] >= 0xB0u && src[1] <= 0xBFu))
-    {
-        /// а-п
-        *dst++ = *src++;
-        *dst++ = xor_or_identity<!to_lower>(*src++, 0x20);
-    }
-    else if (src[0] == 0xD0u && (src[1] >= 0xA0u && src[1] <= 0xAFu))
-    {
-        /// Р-Я
-        *dst++ = xor_or_identity<to_lower>(*src++, 0x1);
-        *dst++ = xor_or_identity<to_lower>(*src++, 0x20);
-    }
-    else if (src[0] == 0xD1u && (src[1] >= 0x80u && src[1] <= 0x8Fu))
-    {
-        /// р-я
-        *dst++ = xor_or_identity<!to_lower>(*src++, 0x1);
-        *dst++ = xor_or_identity<!to_lower>(*src++, 0x20);
-    }
-}
-
-
-/** If the string contains UTF-8 encoded text, convert it to the lower (upper) case.
-  * Note: It is assumed that after the character is converted to another case,
-  *  the length of its multibyte sequence in UTF-8 does not change.
-  * Otherwise, the behavior is undefined.
-  */
-template <char not_case_lower_bound,
-    char not_case_upper_bound,
-    int to_case(int),
-    void cyrillic_to_case(const UInt8 *&, UInt8 *&)>
+template <char not_case_lower_bound, char not_case_upper_bound, bool upper>
 struct LowerUpperUTF8Impl
 {
     static void vector(
@@ -103,180 +38,46 @@ struct LowerUpperUTF8Impl
             return;
         }
 
-        res_data.resize_exact(data.size());
-        res_offsets.assign(offsets);
-        array(data.data(), data.data() + data.size(), offsets, res_data.data());
+        res_data.resize(data.size());
+        res_offsets.resize_exact(offsets.size());
+
+        String output;
+        size_t curr_offset = 0;
+        for (size_t i = 0; i < offsets.size(); ++i)
+        {
+            const auto * data_start = reinterpret_cast<const char *>(&data[offsets[i - 1]]);
+            size_t size = offsets[i] - offsets[i - 1];
+
+            icu::UnicodeString input(data_start, static_cast<int32_t>(size), "UTF-8");
+            if constexpr (upper)
+                input.toUpper();
+            else
+                input.toLower();
+
+            output.clear();
+            input.toUTF8String(output);
+
+            /// For valid UTF-8 input strings, ICU sometimes produces output with extra '\0's at the end. Only the data before the first
+            /// '\0' is valid. It the input is not valid UTF-8, then the behavior of lower/upperUTF8 is undefined by definition. In this
+            /// case, the behavior is also reasonable.
+            const char * res_end = find_last_not_symbols_or_null<'\0'>(output.data(), output.data() + output.size());
+            size_t valid_size = res_end ? res_end - output.data() + 1 : 0;
+
+            res_data.resize(curr_offset + valid_size + 1);
+            memcpy(&res_data[curr_offset], output.data(), valid_size);
+            res_data[curr_offset + valid_size] = 0;
+
+            curr_offset += valid_size + 1;
+            res_offsets[i] = curr_offset;
+        }
     }
 
     static void vectorFixed(const ColumnString::Chars &, size_t, ColumnString::Chars &, size_t)
     {
         throw Exception(ErrorCodes::BAD_ARGUMENTS, "Functions lowerUTF8 and upperUTF8 cannot work with FixedString argument");
     }
-
-    /** Converts a single code point starting at `src` to desired case, storing result starting at `dst`.
-     *    `src` and `dst` are incremented by corresponding sequence lengths. */
-    static bool toCase(const UInt8 *& src, const UInt8 * src_end, UInt8 *& dst, bool partial)
-    {
-        if (src[0] <= ascii_upper_bound)
-        {
-            if (*src >= not_case_lower_bound && *src <= not_case_upper_bound)
-                *dst++ = *src++ ^ flip_case_mask;
-            else
-                *dst++ = *src++;
-        }
-        else if (src + 1 < src_end
-            && ((src[0] == 0xD0u && (src[1] >= 0x80u && src[1] <= 0xBFu)) || (src[0] == 0xD1u && (src[1] >= 0x80u && src[1] <= 0x9Fu))))
-        {
-            cyrillic_to_case(src, dst);
-        }
-        else if (src + 1 < src_end && src[0] == 0xC2u)
-        {
-            /// Punctuation U+0080 - U+00BF, UTF-8: C2 80 - C2 BF
-            *dst++ = *src++;
-            *dst++ = *src++;
-        }
-        else if (src + 2 < src_end && src[0] == 0xE2u)
-        {
-            /// Characters U+2000 - U+2FFF, UTF-8: E2 80 80 - E2 BF BF
-            *dst++ = *src++;
-            *dst++ = *src++;
-            *dst++ = *src++;
-        }
-        else
-        {
-            size_t src_sequence_length = UTF8::seqLength(*src);
-            /// In case partial buffer was passed (due to SSE optimization)
-            /// we cannot convert it with current src_end, but we may have more
-            /// bytes to convert and eventually got correct symbol.
-            if (partial && src_sequence_length > static_cast<size_t>(src_end - src))
-                return false;
-
-            auto src_code_point = UTF8::convertUTF8ToCodePoint(src, src_end - src);
-            if (src_code_point)
-            {
-                int dst_code_point = to_case(*src_code_point);
-                if (dst_code_point > 0)
-                {
-                    size_t dst_sequence_length = UTF8::convertCodePointToUTF8(dst_code_point, dst, src_end - src);
-                    assert(dst_sequence_length <= 4);
-
-                    /// We don't support cases when lowercase and uppercase characters occupy different number of bytes in UTF-8.
-                    /// As an example, this happens for ß and ẞ.
-                    if (dst_sequence_length == src_sequence_length)
-                    {
-                        src += dst_sequence_length;
-                        dst += dst_sequence_length;
-                        return true;
-                    }
-                }
-            }
-
-            *dst = *src;
-            ++dst;
-            ++src;
-        }
-
-        return true;
-    }
-
-private:
-    static constexpr auto ascii_upper_bound = '\x7f';
-    static constexpr auto flip_case_mask = 'A' ^ 'a';
-
-    static void array(const UInt8 * src, const UInt8 * src_end, const ColumnString::Offsets & offsets, UInt8 * dst)
-    {
-        const auto * offset_it = offsets.begin();
-        const UInt8 * begin = src;
-
-#ifdef __SSE2__
-        static constexpr auto bytes_sse = sizeof(__m128i);
-
-        /// If we are before this position, we can still read at least bytes_sse.
-        const auto * src_end_sse = src_end - bytes_sse + 1;
-
-        /// SSE2 packed comparison operate on signed types, hence compare (c < 0) instead of (c > 0x7f)
-        const auto v_zero = _mm_setzero_si128();
-        const auto v_not_case_lower_bound = _mm_set1_epi8(not_case_lower_bound - 1);
-        const auto v_not_case_upper_bound = _mm_set1_epi8(not_case_upper_bound + 1);
-        const auto v_flip_case_mask = _mm_set1_epi8(flip_case_mask);
-
-        while (src < src_end_sse)
-        {
-            const auto chars = _mm_loadu_si128(reinterpret_cast<const __m128i *>(src));
-
-            /// check for ASCII
-            const auto is_not_ascii = _mm_cmplt_epi8(chars, v_zero);
-            const auto mask_is_not_ascii = _mm_movemask_epi8(is_not_ascii);
-
-            /// ASCII
-            if (mask_is_not_ascii == 0)
-            {
-                const auto is_not_case
-                    = _mm_and_si128(_mm_cmpgt_epi8(chars, v_not_case_lower_bound), _mm_cmplt_epi8(chars, v_not_case_upper_bound));
-                const auto mask_is_not_case = _mm_movemask_epi8(is_not_case);
-
-                /// everything in correct case ASCII
-                if (mask_is_not_case == 0)
-                    _mm_storeu_si128(reinterpret_cast<__m128i *>(dst), chars);
-                else
-                {
-                    /// ASCII in mixed case
-                    /// keep `flip_case_mask` only where necessary, zero out elsewhere
-                    const auto xor_mask = _mm_and_si128(v_flip_case_mask, is_not_case);
-
-                    /// flip case by applying calculated mask
-                    const auto cased_chars = _mm_xor_si128(chars, xor_mask);
-
-                    /// store result back to destination
-                    _mm_storeu_si128(reinterpret_cast<__m128i *>(dst), cased_chars);
-                }
-
-                src += bytes_sse;
-                dst += bytes_sse;
-            }
-            else
-            {
-                /// UTF-8
-
-                /// Find the offset of the next string after src
-                size_t offset_from_begin = src - begin;
-                while (offset_from_begin >= *offset_it)
-                    ++offset_it;
-
-                /// Do not allow one row influence another (since row may have invalid sequence, and break the next)
-                const UInt8 * row_end = begin + *offset_it;
-                chassert(row_end >= src);
-                const UInt8 * expected_end = std::min(src + bytes_sse, row_end);
-
-                while (src < expected_end)
-                {
-                    if (!toCase(src, expected_end, dst, /* partial= */ true))
-                    {
-                        /// Fallback to handling byte by byte.
-                        src_end_sse = src;
-                        break;
-                    }
-                }
-            }
-        }
-
-        /// Find the offset of the next string after src
-        size_t offset_from_begin = src - begin;
-        while (offset_it != offsets.end() && offset_from_begin >= *offset_it)
-            ++offset_it;
-#endif
-
-        /// handle remaining symbols, row by row (to avoid influence of bad UTF8 symbols from one row, to another)
-        while (src < src_end)
-        {
-            const UInt8 * row_end = begin + *offset_it;
-            chassert(row_end >= src);
-
-            while (src < row_end)
-                toCase(src, row_end, dst, /* partial= */ false);
-            ++offset_it;
-        }
-    }
 };
 
 }
+
+#endif
diff --git a/src/Functions/initcapUTF8.cpp b/src/Functions/initcapUTF8.cpp
index 282d846094e..004586dce26 100644
--- a/src/Functions/initcapUTF8.cpp
+++ b/src/Functions/initcapUTF8.cpp
@@ -1,9 +1,8 @@
 #include <DataTypes/DataTypeString.h>
 #include <Functions/FunctionStringToString.h>
-#include <Functions/LowerUpperUTF8Impl.h>
 #include <Functions/FunctionFactory.h>
 #include <Poco/Unicode.h>
-
+#include <Common/UTF8Helpers.h>
 
 namespace DB
 {
diff --git a/src/Functions/lowerUTF8.cpp b/src/Functions/lowerUTF8.cpp
index 7adb0069121..e2f7cb84730 100644
--- a/src/Functions/lowerUTF8.cpp
+++ b/src/Functions/lowerUTF8.cpp
@@ -1,9 +1,10 @@
-#include <DataTypes/DataTypeString.h>
+#include "config.h"
+
+#if USE_ICU
+
+#include <Functions/FunctionFactory.h>
 #include <Functions/FunctionStringToString.h>
 #include <Functions/LowerUpperUTF8Impl.h>
-#include <Functions/FunctionFactory.h>
-#include <Poco/Unicode.h>
-
 
 namespace DB
 {
@@ -15,13 +16,25 @@ struct NameLowerUTF8
     static constexpr auto name = "lowerUTF8";
 };
 
-using FunctionLowerUTF8 = FunctionStringToString<LowerUpperUTF8Impl<'A', 'Z', Poco::Unicode::toLower, UTF8CyrillicToCase<true>>, NameLowerUTF8>;
+using FunctionLowerUTF8 = FunctionStringToString<LowerUpperUTF8Impl<'A', 'Z', false>, NameLowerUTF8>;
 
 }
 
 REGISTER_FUNCTION(LowerUTF8)
 {
-    factory.registerFunction<FunctionLowerUTF8>();
+    FunctionDocumentation::Description description
+        = R"(Converts a string to lowercase, assuming that the string contains valid UTF-8 encoded text. If this assumption is violated, no exception is thrown and the result is undefined.)";
+    FunctionDocumentation::Syntax syntax = "lowerUTF8(input)";
+    FunctionDocumentation::Arguments arguments = {{"input", "Input with String type"}};
+    FunctionDocumentation::ReturnedValue returned_value = "A String data type value";
+    FunctionDocumentation::Examples examples = {
+        {"first", "SELECT lowerUTF8('München') as Lowerutf8;", "münchen"},
+    };
+    FunctionDocumentation::Categories categories = {"String"};
+
+    factory.registerFunction<FunctionLowerUTF8>({description, syntax, arguments, returned_value, examples, categories});
 }
 
 }
+
+#endif
diff --git a/src/Functions/upperUTF8.cpp b/src/Functions/upperUTF8.cpp
index 659e67f0ef3..ef26430331f 100644
--- a/src/Functions/upperUTF8.cpp
+++ b/src/Functions/upperUTF8.cpp
@@ -1,8 +1,10 @@
+#include "config.h"
+
+#if USE_ICU
+
+#include <Functions/FunctionFactory.h>
 #include <Functions/FunctionStringToString.h>
 #include <Functions/LowerUpperUTF8Impl.h>
-#include <Functions/FunctionFactory.h>
-#include <Poco/Unicode.h>
-
 
 namespace DB
 {
@@ -14,13 +16,25 @@ struct NameUpperUTF8
     static constexpr auto name = "upperUTF8";
 };
 
-using FunctionUpperUTF8 = FunctionStringToString<LowerUpperUTF8Impl<'a', 'z', Poco::Unicode::toUpper, UTF8CyrillicToCase<false>>, NameUpperUTF8>;
+using FunctionUpperUTF8 = FunctionStringToString<LowerUpperUTF8Impl<'a', 'z', true>, NameUpperUTF8>;
 
 }
 
 REGISTER_FUNCTION(UpperUTF8)
 {
-    factory.registerFunction<FunctionUpperUTF8>();
+    FunctionDocumentation::Description description
+        = R"(Converts a string to lowercase, assuming that the string contains valid UTF-8 encoded text. If this assumption is violated, no exception is thrown and the result is undefined.)";
+    FunctionDocumentation::Syntax syntax = "upperUTF8(input)";
+    FunctionDocumentation::Arguments arguments = {{"input", "Input with String type"}};
+    FunctionDocumentation::ReturnedValue returned_value = "A String data type value";
+    FunctionDocumentation::Examples examples = {
+        {"first", "SELECT upperUTF8('München') as Upperutf8;", "MÜNCHEN"},
+    };
+    FunctionDocumentation::Categories categories = {"String"};
+
+    factory.registerFunction<FunctionUpperUTF8>({description, syntax, arguments, returned_value, examples, categories});
 }
 
 }
+
+#endif
diff --git a/tests/queries/0_stateless/00170_lower_upper_utf8.reference b/tests/queries/0_stateless/00170_lower_upper_utf8.reference
index f202cb75513..3c644f22b9b 100644
--- a/tests/queries/0_stateless/00170_lower_upper_utf8.reference
+++ b/tests/queries/0_stateless/00170_lower_upper_utf8.reference
@@ -22,3 +22,7 @@
 1
 1
 1
+1
+1
+1
+1
diff --git a/tests/queries/0_stateless/00170_lower_upper_utf8.sql b/tests/queries/0_stateless/00170_lower_upper_utf8.sql
index 4caba2033ff..85b6c5c6095 100644
--- a/tests/queries/0_stateless/00170_lower_upper_utf8.sql
+++ b/tests/queries/0_stateless/00170_lower_upper_utf8.sql
@@ -1,3 +1,6 @@
+-- Tags: no-fasttest
+-- no-fasttest: upper/lowerUTF8 use ICU
+
 select lower('aaaaaaaaaaaaaaa012345789,.!aaaa' as str) = str;
 select lowerUTF8('aaaaaaaaaaaaaaa012345789,.!aaaa' as str) = str;
 select lower('AaAaAaAaAaAaAaA012345789,.!aAaA') = 'aaaaaaaaaaaaaaa012345789,.!aaaa';
@@ -27,3 +30,11 @@ select sum(lower(materialize('aaaaАБВГAAAAaaAA')) = materialize('aaaaАБВ
 select sum(upper(materialize('aaaaАБВГAAAAaaAA')) = materialize('AAAAАБВГAAAAAAAA')) = count() from system.one array join range(16384) as n;
 select sum(lowerUTF8(materialize('aaaaАБВГAAAAaaAA')) = materialize('aaaaабвгaaaaaaaa')) = count() from system.one array join range(16384) as n;
 select sum(upperUTF8(materialize('aaaaАБВГAAAAaaAA')) = materialize('AAAAАБВГAAAAAAAA')) = count() from system.one array join range(16384) as n;
+
+-- Turkish language
+select upperUTF8('ır') = 'IR';
+select lowerUTF8('ır') = 'ır';
+
+-- German language
+select upper('öäüß') = 'öäüß';
+select lower('ÖÄÜẞ') = 'ÖÄÜẞ';
diff --git a/tests/queries/0_stateless/00233_position_function_family.sql b/tests/queries/0_stateless/00233_position_function_family.sql
index dd7394bc39a..d6668cb7ba4 100644
--- a/tests/queries/0_stateless/00233_position_function_family.sql
+++ b/tests/queries/0_stateless/00233_position_function_family.sql
@@ -1,3 +1,6 @@
+-- Tags: no-fasttest
+-- no-fasttest: upper/lowerUTF8 use ICU
+
 SET send_logs_level = 'fatal';
 
 select 1 = position('', '');
diff --git a/tests/queries/0_stateless/00761_lower_utf8_bug.sql b/tests/queries/0_stateless/00761_lower_utf8_bug.sql
index de20b894331..a0ab55edc15 100644
--- a/tests/queries/0_stateless/00761_lower_utf8_bug.sql
+++ b/tests/queries/0_stateless/00761_lower_utf8_bug.sql
@@ -1 +1,4 @@
+-- Tags: no-fasttest
+-- no-fasttest: upper/lowerUTF8 use ICU
+
 SELECT lowerUTF8('\xF0') = lowerUTF8('\xF0');
diff --git a/tests/queries/0_stateless/01278_random_string_utf8.sql b/tests/queries/0_stateless/01278_random_string_utf8.sql
index da2dc48c3e1..290d6a0c759 100644
--- a/tests/queries/0_stateless/01278_random_string_utf8.sql
+++ b/tests/queries/0_stateless/01278_random_string_utf8.sql
@@ -1,3 +1,6 @@
+-- Tags: no-fasttest
+-- no-fasttest: upper/lowerUTF8 use ICU
+
 SELECT randomStringUTF8('string'); -- { serverError ILLEGAL_TYPE_OF_ARGUMENT }
 SELECT lengthUTF8(randomStringUTF8(100));
 SELECT toTypeName(randomStringUTF8(10));
diff --git a/tests/queries/0_stateless/01431_utf8_ubsan.reference b/tests/queries/0_stateless/01431_utf8_ubsan.reference
index c98c950d535..dc785e57851 100644
--- a/tests/queries/0_stateless/01431_utf8_ubsan.reference
+++ b/tests/queries/0_stateless/01431_utf8_ubsan.reference
@@ -1,2 +1,2 @@
-FF
-FF
+EFBFBD
+EFBFBD
diff --git a/tests/queries/0_stateless/01431_utf8_ubsan.sql b/tests/queries/0_stateless/01431_utf8_ubsan.sql
index d6a299225b1..3a28e023805 100644
--- a/tests/queries/0_stateless/01431_utf8_ubsan.sql
+++ b/tests/queries/0_stateless/01431_utf8_ubsan.sql
@@ -1,2 +1,5 @@
+-- Tags: no-fasttest
+-- no-fasttest: upper/lowerUTF8 use ICU
+
 SELECT hex(lowerUTF8('\xFF'));
 SELECT hex(upperUTF8('\xFF'));
diff --git a/tests/queries/0_stateless/01590_countSubstrings.sql b/tests/queries/0_stateless/01590_countSubstrings.sql
index b38cbb7d188..5ec4f412d7f 100644
--- a/tests/queries/0_stateless/01590_countSubstrings.sql
+++ b/tests/queries/0_stateless/01590_countSubstrings.sql
@@ -1,3 +1,6 @@
+-- Tags: no-fasttest
+-- no-fasttest: upper/lowerUTF8 use ICU
+
 --
 -- countSubstrings
 --
diff --git a/tests/queries/0_stateless/02071_lower_upper_utf8_row_overlaps.reference b/tests/queries/0_stateless/02071_lower_upper_utf8_row_overlaps.reference
index a3bac432482..deabef61a88 100644
--- a/tests/queries/0_stateless/02071_lower_upper_utf8_row_overlaps.reference
+++ b/tests/queries/0_stateless/02071_lower_upper_utf8_row_overlaps.reference
@@ -5,9 +5,9 @@ insert into utf8_overlap values ('\xe2'), ('Foo⚊BarBazBam'), ('\xe2'), ('Foo
 --                                             MONOGRAM FOR YANG
 with lowerUTF8(str) as l_, upperUTF8(str) as u_, '0x' || hex(str) as h_
 select length(str), if(l_ == '\xe2', h_, l_), if(u_ == '\xe2', h_, u_) from utf8_overlap format CSV;
-1,"0xE2","0xE2"
+1,"�","�"
 15,"foo⚊barbazbam","FOO⚊BARBAZBAM"
-1,"0xE2","0xE2"
+1,"�","�"
 15,"foo⚊barbazbam","FOO⚊BARBAZBAM"
 -- NOTE: regression test for introduced bug
 -- https://github.com/ClickHouse/ClickHouse/issues/42756
diff --git a/tests/queries/0_stateless/02071_lower_upper_utf8_row_overlaps.sql b/tests/queries/0_stateless/02071_lower_upper_utf8_row_overlaps.sql
index 8ca0a3f5f75..d175e0659d0 100644
--- a/tests/queries/0_stateless/02071_lower_upper_utf8_row_overlaps.sql
+++ b/tests/queries/0_stateless/02071_lower_upper_utf8_row_overlaps.sql
@@ -1,3 +1,6 @@
+-- Tags: no-fasttest
+-- no-fasttest: upper/lowerUTF8 use ICU
+
 drop table if exists utf8_overlap;
 create table utf8_overlap (str String) engine=Memory();
 
diff --git a/tests/queries/0_stateless/02415_all_new_functions_must_be_documented.reference b/tests/queries/0_stateless/02415_all_new_functions_must_be_documented.reference
index c39f1fb1ce9..0980e25b70f 100644
--- a/tests/queries/0_stateless/02415_all_new_functions_must_be_documented.reference
+++ b/tests/queries/0_stateless/02415_all_new_functions_must_be_documented.reference
@@ -416,7 +416,6 @@ logTrace
 lowCardinalityIndices
 lowCardinalityKeys
 lower
-lowerUTF8
 makeDate
 makeDate32
 makeDateTime
@@ -897,7 +896,6 @@ tupleToNameValuePairs
 unbin
 unhex
 upper
-upperUTF8
 uptime
 validateNestedArraySizes
 version
diff --git a/tests/queries/0_stateless/02514_if_with_lazy_low_cardinality.sql b/tests/queries/0_stateless/02514_if_with_lazy_low_cardinality.sql
index 80e3c0a9ece..b169cfd0ab9 100644
--- a/tests/queries/0_stateless/02514_if_with_lazy_low_cardinality.sql
+++ b/tests/queries/0_stateless/02514_if_with_lazy_low_cardinality.sql
@@ -1,3 +1,6 @@
+-- Tags: no-fasttest
+-- no-fasttest: upper/lowerUTF8 use ICU
+
 create table if not exists t (`arr.key` Array(LowCardinality(String)), `arr.value` Array(LowCardinality(String))) engine = Memory;
 insert into t (`arr.key`, `arr.value`) values (['a'], ['b']);
 select if(true, if(lowerUTF8(arr.key) = 'a', 1, 2), 3) as x from t left array join arr;
diff --git a/tests/queries/0_stateless/02807_lower_utf8_msan.sql b/tests/queries/0_stateless/02807_lower_utf8_msan.sql
index e9eb18bf615..95f224577f7 100644
--- a/tests/queries/0_stateless/02807_lower_utf8_msan.sql
+++ b/tests/queries/0_stateless/02807_lower_utf8_msan.sql
@@ -1,2 +1,5 @@
+-- Tags: no-fasttest
+-- no-fasttest: upper/lowerUTF8 use ICU
+
 SELECT lowerUTF8(arrayJoin(['©--------------------------------------', '©--------------------'])) ORDER BY 1;
 SELECT upperUTF8(materialize('aaaaАБВГaaaaaaaaaaaaАБВГAAAAaaAA')) FROM numbers(2);
diff --git a/tests/queries/0_stateless/03015_peder1001.sql b/tests/queries/0_stateless/03015_peder1001.sql
index 810503207f2..df8e4db1536 100644
--- a/tests/queries/0_stateless/03015_peder1001.sql
+++ b/tests/queries/0_stateless/03015_peder1001.sql
@@ -1,3 +1,6 @@
+-- Tags: no-fasttest
+-- no-fasttest: upper/lowerUTF8 use ICU
+
 DROP TABLE IF EXISTS test_data;
 
 CREATE TABLE test_data