diff --git a/CMakeLists.txt b/CMakeLists.txt
index fcf72fa..a028645 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -32,7 +32,8 @@ target_sources(
               FILES
               include/conc/atomic.hpp
               include/conc/concepts.hpp
-              include/conc/concurrency.hpp)
+              include/conc/concurrency.hpp
+              include/conc/detail/freestanding.hpp)
 
 if(PROJECT_IS_TOP_LEVEL)
     add_docs(docs)
diff --git a/include/conc/concurrency.hpp b/include/conc/concurrency.hpp
index 8fa5865..563a855 100644
--- a/include/conc/concurrency.hpp
+++ b/include/conc/concurrency.hpp
@@ -1,13 +1,14 @@
 #pragma once
 
-#ifdef SIMULATE_FREESTANDING
+#include <conc/concepts.hpp>
+#include <conc/detail/freestanding.hpp>
+
+#ifdef CONC_FREESTANDING
 #define HAS_MUTEX 0
 #else
 #define HAS_MUTEX __has_include(<mutex>)
 #endif
 
-#include <conc/concepts.hpp>
-
 #if HAS_MUTEX
 #include <mutex>
 #endif
diff --git a/include/conc/detail/freestanding.hpp b/include/conc/detail/freestanding.hpp
new file mode 100644
index 0000000..8cf5c7b
--- /dev/null
+++ b/include/conc/detail/freestanding.hpp
@@ -0,0 +1,5 @@
+#pragma once
+
+#ifdef SIMULATE_FREESTANDING
+#define CONC_FREESTANDING
+#endif
diff --git a/test/fail_no_conc_policy.cpp b/test/fail_no_conc_policy.cpp
index 2f20c26..53b2768 100644
--- a/test/fail_no_conc_policy.cpp
+++ b/test/fail_no_conc_policy.cpp
@@ -1,4 +1,4 @@
-#define SIMULATE_FREESTANDING
+#define CONC_FREESTANDING
 
 #include <conc/concurrency.hpp>
 
diff --git a/test/freestanding_conc_injected_policy.cpp b/test/freestanding_conc_injected_policy.cpp
index 07027c1..621a2b0 100644
--- a/test/freestanding_conc_injected_policy.cpp
+++ b/test/freestanding_conc_injected_policy.cpp
@@ -1,4 +1,4 @@
-#define SIMULATE_FREESTANDING
+#define CONC_FREESTANDING
 
 #include <conc/concepts.hpp>
 #include <conc/concurrency.hpp>