diff --git a/include/openlibm_math.h b/include/openlibm_math.h
index 4d53605..81d5843 100644
--- a/include/openlibm_math.h
+++ b/include/openlibm_math.h
@@ -194,6 +194,9 @@ extern int signgam;
 #if defined(__cplusplus)
 extern "C" {
 #endif
+/* Symbol present when OpenLibm is used. */
+int isopenlibm(void);
+
 /*
  * ANSI/POSIX
  */
diff --git a/src/common.c b/src/common.c
index 5905c20..373f579 100644
--- a/src/common.c
+++ b/src/common.c
@@ -1,6 +1,6 @@
-#include "math_private.h"
+#include <openlibm_math.h>
 
-DLLEXPORT int isopenlibm(void);
+#include "math_private.h"
 
 DLLEXPORT int isopenlibm(void) {
     return 1;