diff --git a/include/ruby/win32.h b/include/ruby/win32.h
index ca99ee48f3..a2ba226b59 100644
--- a/include/ruby/win32.h
+++ b/include/ruby/win32.h
@@ -781,7 +781,7 @@ RUBY_SYMBOL_EXPORT_END
 static inline double
 rb_w32_pow(double x, double y)
 {
-    return powl(x, y);
+    return (double)powl(x, y);
 }
 #elif defined(__MINGW64_VERSION_MAJOR)
 double rb_w32_pow(double x, double y);