diff --git a/lib/string.in.h b/lib/string.in.h
--- a/lib/string.in.h
+++ b/lib/string.in.h
@@ -89,7 +89,11 @@
 _GL_EXTERN_C void free (void *);
 # define free rpl_free
 #endif
+#ifndef _MSC_VER
+/* On MSVC the CRT declares free with __declspec(dllimport) linkage.
+   A plain forward declaration here would conflict (C2375).  */
 _GL_EXTERN_C void free (void *);
+#endif
 
 /* Clear a block of memory.  The compiler will not delete a call to
    this function, even if the block is dead after the call.  */