Index: cmake/compiler_flags/GNU_C.cmake
--- cmake/compiler_flags/GNU_C.cmake.orig
+++ cmake/compiler_flags/GNU_C.cmake
@@ -6,7 +6,7 @@
 # granted to it by virtue of its status as an intergovernmental organisation
 # nor does it submit to any jurisdiction.
 
-set( CMAKE_C_FLAGS_RELEASE        "-O3 -DNDEBUG"    CACHE STRING "C compiler flags for Release builds"          FORCE )
+set( CMAKE_C_FLAGS_RELEASE        "-DNDEBUG"    CACHE STRING "C compiler flags for Release builds"          FORCE )
 set( CMAKE_C_FLAGS_BIT            "-O2 -DNDEBUG"    CACHE STRING "C compiler flags for Bit-reproducible builds" FORCE )
 set( CMAKE_C_FLAGS_DEBUG          "-O0 -g"          CACHE STRING "C compiler flags for Debug builds"            FORCE )
 set( CMAKE_C_FLAGS_PRODUCTION     "-O2 -g"          CACHE STRING "C compiler flags for Production builds."      FORCE )
