diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 874eabfaa13..f12e6db8642 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -138,17 +138,6 @@ int main() {
 }
 " HAVE_STDLIB_MAP_SPLICING)
 
-if(CMAKE_COMPILER_IS_GNUCXX AND
-    CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.1)
-  # this is not always correct, as one can use clang with libstdc++ or
-  # use old gcc with new libstdc++, but it covers the most cases.
-  #
-  # libstdc++ 4.9 has O(n) list::size(), and its regex is buggy
-  message(SEND_ERROR "performance regression is expected due to an O(n) "
-    "implementation of 'std::list::size()' in libstdc++ older than 5.1.0, "
-    "Please use GCC 5.1 and up.")
-endif()
-
 ## Handle diagnostics color if compiler supports them.
 CHECK_C_COMPILER_FLAG("-fdiagnostics-color=always"
   COMPILER_SUPPORTS_DIAGNOSTICS_COLOR)