diff --git a/Source/WebCore/ChangeLog b/Source/WebCore/ChangeLog
index acb74726c4272..350b4c036c2f9 100644
--- a/Source/WebCore/ChangeLog
+++ b/Source/WebCore/ChangeLog
@@ -1,3 +1,17 @@
+2015-01-01  Chris Dumez  <cdumez@apple.com>
+
+        ASSERT that a null key is never used with FeatureCounter
+        https://bugs.webkit.org/show_bug.cgi?id=140030
+
+        Reviewed by Darin Adler.
+
+        * platform/FeatureCounter.cpp:
+        (WebCore::FeatureCounter::incrementKey):
+        (WebCore::FeatureCounter::setKey):
+        * platform/ios/FeatureCounter.mm:
+        (WebCore::FeatureCounter::incrementKey):
+        (WebCore::FeatureCounter::setKey):
+
 2015-01-01  Chris Dumez  <cdumez@apple.com>
 
         [iOS] Fix memory leak in FeatureCounter
diff --git a/Source/WebCore/platform/FeatureCounter.cpp b/Source/WebCore/platform/FeatureCounter.cpp
index 8c37d2835bd9f..212d06d4e7786 100644
--- a/Source/WebCore/platform/FeatureCounter.cpp
+++ b/Source/WebCore/platform/FeatureCounter.cpp
@@ -52,13 +52,13 @@ bool FeatureCounter::shouldUseForPage(Page* page)
 void FeatureCounter::incrementKey(Page* page, const char* const key)
 {
     UNUSED_PARAM(page);
-    UNUSED_PARAM(key);
+    ASSERT_UNUSED(key, key);
 }
 
 void FeatureCounter::setKey(Page* page, const char* const key, int64_t value)
 {
     UNUSED_PARAM(page);
-    UNUSED_PARAM(key);
+    ASSERT_UNUSED(key, key);
     UNUSED_PARAM(value);
 }
 
diff --git a/Source/WebCore/platform/ios/FeatureCounter.mm b/Source/WebCore/platform/ios/FeatureCounter.mm
index 7b269d2435419..3d61f3485747b 100644
--- a/Source/WebCore/platform/ios/FeatureCounter.mm
+++ b/Source/WebCore/platform/ios/FeatureCounter.mm
@@ -34,6 +34,7 @@
 
 void FeatureCounter::incrementKey(Page* page, const char* const key)
 {
+    ASSERT(key);
     if (!shouldUseForPage(page))
         return;
 
@@ -43,6 +44,7 @@
 
 void FeatureCounter::setKey(Page* page, const char* const key, int64_t value)
 {
+    ASSERT(key);
     if (!shouldUseForPage(page))
         return;