diff --git a/src/include/port.h b/src/include/port.h
index 9567590581..aec5281e43 100644
--- a/src/include/port.h
+++ b/src/include/port.h
@@ -355,8 +355,11 @@ extern int	fls(int mask);
 #endif
 
 #ifndef HAVE_GETPEEREID
+/* On Windows, Perl might have incompatible definitions of uid_t and gid_t. */
+#ifndef PLPERL_HAVE_UID_GID
 extern int	getpeereid(int sock, uid_t *uid, gid_t *gid);
 #endif
+#endif
 
 #ifndef HAVE_ISINF
 extern int	isinf(double x);