diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index d90598d66..d03e04701 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,8 @@
+2009-11-16  Eric Blake  <ebb9@byu.net>
+
+	* environ.cc (setenv): Detect invalid argument.
+	(unsetenv): Distinguish EFAULT from EINVAL.
+
 2009-11-13  Corinna Vinschen  <corinna@vinschen.de>
 
 	* net.cc (fdsock): Fill _rmem and _wmem with valid values returned
diff --git a/winsup/cygwin/environ.cc b/winsup/cygwin/environ.cc
index bc1130372..4935bc815 100644
--- a/winsup/cygwin/environ.cc
+++ b/winsup/cygwin/environ.cc
@@ -413,10 +413,11 @@ setenv (const char *name, const char *value, int overwrite)
   myfault efault;
   if (efault.faulted (EFAULT))
     return -1;
-  if (!*name)
-    return 0;
-  if (*value == '=')
-    value++;
+  if (!name || !*name || strchr (name, '='))
+    {
+      set_errno (EINVAL);
+      return -1;
+    }
   return _addenv (name, value, !!overwrite);
 }
 
@@ -427,7 +428,9 @@ unsetenv (const char *name)
   register char **e;
   int offset;
   myfault efault;
-  if (efault.faulted () || *name == '\0' || strchr (name, '='))
+  if (efault.faulted (EFAULT))
+    return -1;
+  if (!name || *name == '\0' || strchr (name, '='))
     {
       set_errno (EINVAL);
       return -1;