diff --git a/pymemcache/client/base.py b/pymemcache/client/base.py
index 05db0818..7dcad12e 100644
--- a/pymemcache/client/base.py
+++ b/pymemcache/client/base.py
@@ -90,29 +90,19 @@ def _check_key(key, allow_unicode_keys, key_prefix=b''):
         try:
             key = key.encode('ascii')
         except (UnicodeEncodeError, UnicodeDecodeError):
-            raise MemcacheIllegalInputError("Non-ASCII key: '%r'" % (key,))
+            raise MemcacheIllegalInputError("Non-ASCII key: '%r'" % key)
+
     key = key_prefix + key
+    parts = key.split()
 
     if len(key) > 250:
-        raise MemcacheIllegalInputError("Key is too long: '%r'" % (key,))
-
-    for c in bytearray(key):
-        if c == ord(b' '):
-            raise MemcacheIllegalInputError(
-                "Key contains space: '%r'" % (key,)
-            )
-        elif c == ord(b'\n'):
-            raise MemcacheIllegalInputError(
-                "Key contains newline: '%r'" % (key,)
-            )
-        elif c == ord(b'\00'):
-            raise MemcacheIllegalInputError(
-                "Key contains null character: '%r'" % (key,)
-            )
-        elif c == ord(b'\r'):
-            raise MemcacheIllegalInputError(
-                "Key contains carriage return: '%r'" % (key,)
-            )
+        raise MemcacheIllegalInputError("Key is too long: '%r'" % key)
+    # second statement catches leading or trailing whitespace
+    elif len(parts) > 1 or parts[0] != key:
+        raise MemcacheIllegalInputError("Key contains whitespace: '%r'" % key)
+    elif b'\00' in key:
+        raise MemcacheIllegalInputError("Key contains null: '%r'" % key)
+
     return key
 
 
@@ -765,6 +755,14 @@ def _fetch_cmd(self, name, keys, expect_cas):
     def _store_cmd(self, name, values, expire, noreply, cas=None):
         cmds = []
         keys = []
+
+        extra = b''
+        if cas is not None:
+            extra += b' ' + cas
+        if noreply:
+            extra += b' noreply'
+        expire = six.text_type(expire).encode('ascii')
+
         for key, data in six.iteritems(values):
             # must be able to reliably map responses back to the original order
             keys.append(key)
@@ -781,15 +779,9 @@ def _store_cmd(self, name, values, expire, noreply, cas=None):
                 except UnicodeEncodeError as e:
                     raise MemcacheIllegalInputError(str(e))
 
-            extra = b''
-            if cas is not None:
-                extra += b' ' + cas
-            if noreply:
-                extra += b' noreply'
-
             cmds.append(name + b' ' + key + b' ' +
                         six.text_type(flags).encode('ascii') +
-                        b' ' + six.text_type(expire).encode('ascii') +
+                        b' ' + expire +
                         b' ' + six.text_type(len(data)).encode('ascii') +
                         extra + b'\r\n' + data + b'\r\n')