diff --git a/mjit.c b/mjit.c
index 49bac227a0..faa31da2a4 100644
--- a/mjit.c
+++ b/mjit.c
@@ -422,7 +422,7 @@ exec_process(const char *path, char *const argv[])
                      : waitpid(pid, &stat, 0);
         if (r == -1) {
             if (errno == EINTR) continue;
-            fprintf(stderr, "[%d] waitpid(%d): %s (SIGCHLD=%d,%u)\n",
+            fprintf(stderr, "[%d] waitpid(%"PRI_PIDT_PREFIX"d): %s (SIGCHLD=%d,%u)\n",
                     getpid(), pid, strerror(errno),
                     RUBY_SIGCHLD, SIGCHLD_LOSSY);
             break;
diff --git a/win32/Makefile.sub b/win32/Makefile.sub
index 20b47a581a..fd852c21b7 100644
--- a/win32/Makefile.sub
+++ b/win32/Makefile.sub
@@ -760,7 +760,7 @@ $(CONFIG_H): $(MKFILES) $(srcdir)/win32/Makefile.sub $(win_srcdir)/Makefile.sub
 #define ssize_t int
 !endif
 #define PRI_LL_PREFIX "I64"
-#define PRI_PIDT_PREFIX PRI_INT_PREFIX
+#define PRI_PIDT_PREFIX "I"
 #define GETGROUPS_T int
 #define RETSIGTYPE void
 #define TYPEOF_TIMEVAL_TV_SEC long