diff --git a/src/racket/include/scheme.h b/src/racket/include/scheme.h
index 66b6eb9a18..39aaccb783 100644
--- a/src/racket/include/scheme.h
+++ b/src/racket/include/scheme.h
@@ -93,6 +93,8 @@ typedef struct {
 # else
 typedef long double mz_long_double;
 # endif
+#else
+typedef double mz_long_double;
 #endif
 
 #ifdef DONT_ITIMER
diff --git a/src/racket/src/numstr.c b/src/racket/src/numstr.c
index 5b29aaa9e6..2484933329 100644
--- a/src/racket/src/numstr.c
+++ b/src/racket/src/numstr.c
@@ -1204,10 +1204,14 @@ Scheme_Object *scheme_read_number(const mzchar *str, intptr_t len,
       && (len <= MAX_FAST_FLOATREAD_LEN)
       && (!is_long_double || MZ_LONG_DOUBLE_AND(1))) {
     double d = 1.0;
-    long_double ld;
+#ifdef MZ_LONG_DOUBLE
+    mz_long_double ld;
+#endif
     GC_CAN_IGNORE char *ptr;
 
+#ifdef MZ_LONG_DOUBLE
     memset(&ld, 0, sizeof(ld)); /* avoid a compiler warning */
+#endif
 
     if (has_expt && !(str[has_expt + 1])) {
       if (report)