diff --git a/src/Common/Allocator.cpp b/src/Common/Allocator.cpp
new file mode 100644
index 00000000000..9de52a6e3f5
--- /dev/null
+++ b/src/Common/Allocator.cpp
@@ -0,0 +1,19 @@
+#include "Allocator.h"
+
+/** Keep definition of this constant in cpp file; otherwise its value
+  * is inlined into allocator code making it impossible to override it
+  * in third-party code.
+  *
+  * Note: extern may seem redundant, but is actually needed due to bug in GCC.
+  * See also: https://gcc.gnu.org/legacy-ml/gcc-help/2017-12/msg00021.html
+  */
+#ifdef NDEBUG
+    __attribute__((__weak__)) extern const size_t MMAP_THRESHOLD = 64 * (1ULL << 20);
+#else
+    /**
+      * In debug build, use small mmap threshold to reproduce more memory
+      * stomping bugs. Along with ASLR it will hopefully detect more issues than
+      * ASan. The program may fail due to the limit on number of memory mappings.
+      */
+    __attribute__((__weak__)) extern const size_t MMAP_THRESHOLD = 4096;
+#endif
diff --git a/src/Common/Allocator.h b/src/Common/Allocator.h
index ead456f935e..a593783a047 100644
--- a/src/Common/Allocator.h
+++ b/src/Common/Allocator.h
@@ -57,16 +57,7 @@
   * third-party applications which may already use own allocator doing mmaps
   * in the implementation of alloc/realloc.
   */
-#ifdef NDEBUG
-    __attribute__((__weak__)) extern const size_t MMAP_THRESHOLD = 64 * (1ULL << 20);
-#else
-    /**
-      * In debug build, use small mmap threshold to reproduce more memory
-      * stomping bugs. Along with ASLR it will hopefully detect more issues than
-      * ASan. The program may fail due to the limit on number of memory mappings.
-      */
-    __attribute__((__weak__)) extern const size_t MMAP_THRESHOLD = 4096;
-#endif
+extern const size_t MMAP_THRESHOLD;
 
 static constexpr size_t MMAP_MIN_ALIGNMENT = 4096;
 static constexpr size_t MALLOC_MIN_ALIGNMENT = 8;
diff --git a/src/Common/ya.make b/src/Common/ya.make
index 327089ff31d..32cb55adf4f 100644
--- a/src/Common/ya.make
+++ b/src/Common/ya.make
@@ -23,6 +23,7 @@ INCLUDE(${ARCADIA_ROOT}/clickhouse/cmake/yandex/ya.make.versions.inc)
 SRCS(
     ActionLock.cpp
     AlignedBuffer.cpp
+    Allocator.cpp
     checkStackSize.cpp
     ClickHouseRevision.cpp
     Config/AbstractConfigurationComparison.cpp