diff --git a/src/core/include/mp-units/bits/core_gmf.h b/src/core/include/mp-units/bits/core_gmf.h
index 3f2953439..f5392c21c 100644
--- a/src/core/include/mp-units/bits/core_gmf.h
+++ b/src/core/include/mp-units/bits/core_gmf.h
@@ -22,9 +22,13 @@
 
 #pragma once
 
+#define MP_UNITS_IN_GMF
+
 #include <mp-units/bits/hacks.h>
 #include <mp-units/compat_macros.h>
 #include <mp-units/ext/contracts.h>
+
+#ifndef MP_UNITS_IMPORT_STD
 #include <array>
 #include <compare>
 #include <concepts>
@@ -46,9 +50,11 @@
 #if __cpp_lib_text_encoding
 #include <text_encoding>
 #endif
+#endif
 
 #if MP_UNITS_HOSTED
 #include <mp-units/ext/format.h>
+#ifndef MP_UNITS_IMPORT_STD
 #include <cmath>
 #include <locale>
 #include <ostream>
@@ -56,3 +62,6 @@
 #include <sstream>
 #include <string>
 #endif
+#endif
+
+#undef MP_UNITS_IN_GMF
diff --git a/src/core/include/mp-units/ext/format.h b/src/core/include/mp-units/ext/format.h
index 382d02a56..5d8c1fd2e 100644
--- a/src/core/include/mp-units/ext/format.h
+++ b/src/core/include/mp-units/ext/format.h
@@ -35,12 +35,14 @@ MP_UNITS_DIAGNOSTIC_IGNORE_UNREACHABLE
 MP_UNITS_DIAGNOSTIC_IGNORE_SHADOW
 #include <fmt/format.h>
 MP_UNITS_DIAGNOSTIC_POP
-#else
+#else  // MP_UNITS_USE_FMTLIB
 #ifdef MP_UNITS_IMPORT_STD
+#ifndef MP_UNITS_IN_GMF
 import std;
-#else
-#include <format>
-#endif
 #endif
+#else  // MP_UNITS_IMPORT_STD
+#include <format>
+#endif  // MP_UNITS_IMPORT_STD
+#endif  // MP_UNITS_USE_FMTLIB
 
 #endif
diff --git a/src/core/mp-units-core.cpp b/src/core/mp-units-core.cpp
index eb0a3c206..f56a846df 100644
--- a/src/core/mp-units-core.cpp
+++ b/src/core/mp-units-core.cpp
@@ -22,9 +22,7 @@
 
 module;
 
-#ifndef MP_UNITS_IMPORT_STD
 #include <mp-units/bits/core_gmf.h>
-#endif
 
 export module mp_units.core;
 
diff --git a/src/systems/mp-units-systems.cpp b/src/systems/mp-units-systems.cpp
index 71ce35c7c..6c2207ee4 100644
--- a/src/systems/mp-units-systems.cpp
+++ b/src/systems/mp-units-systems.cpp
@@ -22,10 +22,8 @@
 
 module;
 
-#ifndef MP_UNITS_IMPORT_STD
 #include <mp-units/bits/core_gmf.h>
 #include <chrono>
-#endif
 
 export module mp_units.systems;