diff --git a/racket/src/rktio/rktio_envvars.c b/racket/src/rktio/rktio_envvars.c
index 6e28b2e0c7..9991dce624 100644
--- a/racket/src/rktio/rktio_envvars.c
+++ b/racket/src/rktio/rktio_envvars.c
@@ -94,13 +94,15 @@ int rktio_setenv(rktio_t *rktio, const char *name, const char *val)
     int r;
 #ifdef SETENV_DROPS_LEADING_EQUAL_SIGN
     char *tmp = NULL;
-    
-    if (val[0] == '=') {
-      intptr_t len = strlen(val);
-      tmp = malloc(len + 2);
-      memcpy(tmp + 1, val, len + 1);
-      tmp[0] = '=';
-      val = tmp;
+
+    if (rktio->macos_kernel_version < 16) {
+      if (val[0] == '=') {
+        intptr_t len = strlen(val);
+        tmp = malloc(len + 2);
+        memcpy(tmp + 1, val, len + 1);
+        tmp[0] = '=';
+        val = tmp;
+      }
     }
 #endif
 
diff --git a/racket/src/rktio/rktio_main.c b/racket/src/rktio/rktio_main.c
index 595c89f998..c57c3519f9 100644
--- a/racket/src/rktio/rktio_main.c
+++ b/racket/src/rktio/rktio_main.c
@@ -2,6 +2,10 @@
 #include "rktio_private.h"
 #include <stdlib.h>
 #include <string.h>
+#ifdef OS_X
+# include <sys/types.h>
+# include <sys/sysctl.h>
+#endif
 
 rktio_t *rktio_init(void)
 {
@@ -33,6 +37,27 @@ rktio_t *rktio_init(void)
 
   rktio_syslog_init(rktio);
 
+#ifdef OS_X
+  {
+    int a[2], i, k = 0;
+    size_t len;
+    char *vers;
+
+    a[0] = CTL_KERN;
+    a[1] = KERN_OSRELEASE;
+    sysctl(a, 2, NULL, &len, NULL, 0);
+    vers = malloc(len * sizeof(char));
+    sysctl(a, 2, vers, &len, NULL, 0);
+
+    for (i = 0; (i < len) && (vers[i] != '.'); i++)
+      k = (k * 10) + vers[i] - '0';
+
+    rktio->macos_kernel_version = k;
+
+    free(vers);
+  }
+#endif
+
   return rktio;
 }
 
diff --git a/racket/src/rktio/rktio_private.h b/racket/src/rktio/rktio_private.h
index b6267b4f54..54cc9fa38d 100644
--- a/racket/src/rktio/rktio_private.h
+++ b/racket/src/rktio/rktio_private.h
@@ -116,6 +116,10 @@ struct rktio_t {
 #ifdef SUPPORT_BACKGROUND_SLEEP_THREAD
   struct background_sleep_t *background;
 #endif
+
+#ifdef OS_X
+  int macos_kernel_version; /* e.g., 10 => 10.6, 15 => 10.11 */
+#endif
 };
 
 /*========================================================================*/
diff --git a/racket/src/rktio/rktio_time.c b/racket/src/rktio/rktio_time.c
index b034d958eb..442f4491b5 100644
--- a/racket/src/rktio/rktio_time.c
+++ b/racket/src/rktio/rktio_time.c
@@ -262,38 +262,22 @@ static int is_day_before(SYSTEMTIME *a, SYSTEMTIME *b)
 
 #if defined(OS_X) && defined(__x86_64__)
 /* work around a bug in localtime() in 10.6.8 */
-# include <sys/param.h>
-# include <sys/sysctl.h>
-static int VALID_TIME_RANGE(intptr_t lnow)
+static int valid_time_range(rktio_t *rktio, intptr_t lnow)
 {
   /* Fits in 32 bits? */
   int ilnow = (int)lnow;
   if (lnow == (intptr_t)ilnow)
     return 1;
 
-  /* 10.7 or later? */
-  {
-    int a[2];
-    size_t len;
-    char *vers;
-
-    a[0] = CTL_KERN;
-    a[1] = KERN_OSRELEASE;
-    sysctl(a, 2, NULL, &len, NULL, 0);
-    vers = malloc(len * sizeof(char));
-    sysctl(a, 2, vers, &len, NULL, 0);
-
-    if ((vers[0] == '1') && (vers[1] == '0') && (vers[2] == '.')) {
-      /* localtime() in 10.6.x (= 10.x at the kernel layer) doesn't seem
-         to work right with negative numbers that don't fit into 32 bits */
-      free(vers);
-      return 0;
-    }
-    free(vers);
+  if (rktio->macos_kernel_version == 10) {
+    /* localtime() in 10.6.x (= 10.x at the kernel layer) doesn't seem
+       to work right with negative numbers that don't fit into 32 bits */
+    return 0;
   }
 
   return 1;
 }
+# define VALID_TIME_RANGE(lnow) valid_time_range(rktio, lnow)
 #else
 
 # ifdef MIN_VALID_DATE_SECONDS