diff --git a/fw/coroutine.h b/fw/coroutine.h
index 9e6af9e..7a79a10 100644
--- a/fw/coroutine.h
+++ b/fw/coroutine.h
@@ -113,6 +113,18 @@
  */
 
 
+#if defined(__GNUC__) && !defined(__STRICT_ANSI__)
+	// GCC: the extension is always present unless strict ANSI mode is forced.
+	// (Even with -pedantic it still works, just warns.)
+	#define HAVE_LABELS_AS_VALUES 1
+#elif __has_extension(c_labels_as_values)
+	#define HAVE_LABELS_AS_VALUES 1
+#else
+	#define HAVE_LABELS_AS_VALUES 0
+#endif
+
+_Static_assert(HAVE_LABELS_AS_VALUES, "This library requires the GNU C 'labels as values' extension");
+
 // Useful macros
 #define CORO_CONCAT2(s1, s2) s1##s2
 #define CORO_CONCAT(s1, s2) CORO_CONCAT2(s1, s2)
diff --git a/fw/main.c b/fw/main.c
index c6aba2a..4f1112a 100644
--- a/fw/main.c
+++ b/fw/main.c
@@ -10,6 +10,7 @@
 #include "sc7a20.h"
 #include "pd.h"
 #include "fpmath.h"
+#include "coroutine.h"
 
 
 // constants