diff --git a/CMakeLists.txt b/CMakeLists.txt
index 059b15023845..c28ff071b352 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -69,8 +69,6 @@ function(add_module_library name)
     target_compile_options(${name} PUBLIC -fmodules-ts)
   endif ()
 
-  target_compile_definitions(${name} PRIVATE FMT_MODULE)
-
   if (FMT_USE_CMAKE_MODULES)
     target_sources(${name} PUBLIC FILE_SET fmt TYPE CXX_MODULES
                    FILES ${sources})
diff --git a/include/fmt/base.h b/include/fmt/base.h
index c1d09c6d4712..b832e5348226 100644
--- a/include/fmt/base.h
+++ b/include/fmt/base.h
@@ -299,7 +299,7 @@
 
 // Enable minimal optimizations for more compact code in debug mode.
 FMT_PRAGMA_GCC(push_options)
-#if !defined(__OPTIMIZE__) && !defined(__CUDACC__)
+#if !defined(__OPTIMIZE__) && !defined(__CUDACC__) && !defined(FMT_MODULE)
 FMT_PRAGMA_GCC(optimize("Og"))
 #endif
 FMT_PRAGMA_CLANG(diagnostic push)
diff --git a/src/fmt.cc b/src/fmt.cc
index 2dc4ef2f64d9..671fd69589eb 100644
--- a/src/fmt.cc
+++ b/src/fmt.cc
@@ -1,5 +1,7 @@
 module;
 
+#define FMT_MODULE
+
 #ifdef _MSVC_LANG
 #  define FMT_CPLUSPLUS _MSVC_LANG
 #else