--- a/libpng/pngtclDecls.h	2020-04-13 20:16:18.542559383 +0200
+++ b/libpng/pngtclDecls.h	2020-04-13 20:16:33.921314336 +0200
@@ -1369,6 +1369,8 @@
 
 #ifdef __cplusplus
 extern "C" {
+#else
+extern
 #endif
 PNG_IMPEXP const PngtclStubs *pngtclStubsPtr;
 #ifdef __cplusplus