diff --git a/src/if_ruby.c b/src/if_ruby.c
index e989c01..6773a2a 100644
--- a/src/if_ruby.c
+++ b/src/if_ruby.c
@@ -100,7 +100,8 @@
 #endif
 
 // On macOS pre-installed Ruby defines "SIZEOF_TIME_T" as "SIZEOF_LONG" so it
-// conflicts with the definition in config.h then causes macro-redifned warning.
+// conflicts with the definition in config.h then causes a macro-redefined
+// warning.
 #ifdef SIZEOF_TIME_T
 # undef SIZEOF_TIME_T
 #endif
@@ -113,6 +114,11 @@
 # include <st.h>  // for ST_STOP and ST_CONTINUE
 #endif
 
+// See above.
+#ifdef SIZEOF_TIME_T
+# undef SIZEOF_TIME_T
+#endif
+
 #undef off_t	// ruby defines off_t as _int64, Mingw uses long
 #undef EXTERN
 #undef _