diff --git a/src/core/capi.c b/src/core/capi.c
index d59a27e0..182fc35a 100644
--- a/src/core/capi.c
+++ b/src/core/capi.c
@@ -31,11 +31,14 @@
 #ifndef JANET_SINGLE_THREADED
 #ifndef JANET_WINDOWS
 #include <pthread.h>
-#else
-#include <windows.h>
 #endif
 #endif
 
+/* Even if single threaded, include this for atomics! */
+#ifdef JANET_WINDOWS
+#include <windows.h>
+#endif
+
 #ifdef JANET_USE_STDATOMIC
 #include <stdatomic.h>
 /* We don't need stdatomic on most compilers since we use compiler builtins for atomic operations.