diff --git a/spec/rubyspec/optional/capi/ext/thread_spec.c b/spec/rubyspec/optional/capi/ext/thread_spec.c
index 78e8183129..d2e937fd2a 100644
--- a/spec/rubyspec/optional/capi/ext/thread_spec.c
+++ b/spec/rubyspec/optional/capi/ext/thread_spec.c
@@ -7,6 +7,9 @@
 #if HAVE_UNISTD_H
 #include <unistd.h>
 #endif
+#if defined(_WIN32)
+#define pipe(p) rb_w32_pipe(p)
+#endif
 
 #ifdef __cplusplus
 extern "C" {