diff --git a/src/utils/combineReducers.js b/src/utils/combineReducers.js
index 540156f4f0..96412a460d 100644
--- a/src/utils/combineReducers.js
+++ b/src/utils/combineReducers.js
@@ -5,7 +5,7 @@ import pick from '../utils/pick';
 
 /* eslint-disable no-console */
 
-function getErrorMessage(key, action) {
+function getUndefinedStateErrorMessage(key, action) {
   var actionType = action && action.type;
   var actionName = actionType && `"${actionType.toString()}"` || 'an action';
 
@@ -15,28 +15,26 @@ function getErrorMessage(key, action) {
   );
 }
 
-function verifyStateShape(inputState, outputState, action) {
+function getUnexpectedStateKeyWarningMessage(inputState, outputState, action) {
   var reducerKeys = Object.keys(outputState);
   var argumentName = action && action.type === ActionTypes.INIT ?
     'initialState argument passed to createStore' :
     'previous state received by the reducer';
 
   if (reducerKeys.length === 0) {
-    console.error(
+    return (
       'Store does not have a valid reducer. Make sure the argument passed ' +
       'to combineReducers is an object whose values are reducers.'
     );
-    return;
   }
 
   if (!isPlainObject(inputState)) {
-    console.error(
+    return (
       `The ${argumentName} has unexpected type of "` +
       ({}).toString.call(inputState).match(/\s([a-z|A-Z]+)/)[1] +
       `". Expected argument to be an object with the following ` +
       `keys: "${reducerKeys.join('", "')}"`
     );
-    return;
   }
 
   var unexpectedKeys = Object.keys(inputState).filter(
@@ -44,7 +42,7 @@ function verifyStateShape(inputState, outputState, action) {
   );
 
   if (unexpectedKeys.length > 0) {
-    console.error(
+    return (
       `Unexpected ${unexpectedKeys.length > 1 ? 'keys' : 'key'} ` +
       `"${unexpectedKeys.join('", "')}" found in ${argumentName}. ` +
       `Expected to find one of the known reducer keys instead: ` +
@@ -53,6 +51,34 @@ function verifyStateShape(inputState, outputState, action) {
   }
 }
 
+function assertReducerSanity(reducers) {
+  Object.keys(reducers).forEach(key => {
+    var reducer = reducers[key];
+    var initialState = reducer(undefined, { type: ActionTypes.INIT });
+
+    if (typeof initialState === 'undefined') {
+      throw new Error(
+        `Reducer "${key}" returned undefined during initialization. ` +
+        `If the state passed to the reducer is undefined, you must ` +
+        `explicitly return the initial state. The initial state may ` +
+        `not be undefined.`
+      );
+    }
+
+    var type = '@@redux/PROBE_UNKNOWN_ACTION_' + Math.random().toString(36).substring(7).split('').join('.');
+    if (typeof reducer(undefined, { type }) === 'undefined') {
+      throw new Error(
+        `Reducer "${key}" returned undefined when probed with a random type. ` +
+        `Don't try to handle ${ActionTypes.INIT} or other actions in "redux/*" ` +
+        `namespace. They are considered private. Instead, you must return the ` +
+        `current state for any unknown actions, unless it is undefined, ` +
+        `in which case you must return the initial state, regardless of the ` +
+        `action type. The initial state may not be undefined.`
+      );
+    }
+  });
+}
+
 /**
  * Turns an object whose values are different reducer functions, into a single
  * reducer function. It will call every child reducer, and gather their results
@@ -74,37 +100,11 @@ export default function combineReducers(reducers) {
   var finalReducers = pick(reducers, (val) => typeof val === 'function');
   var sanityError;
 
-  Object.keys(finalReducers).forEach(key => {
-    var reducer = finalReducers[key];
-    var initialState;
-
-    try {
-      initialState = reducer(undefined, { type: ActionTypes.INIT });
-    } catch (e) {
-      sanityError = e;
-    }
-
-    if (!sanityError && typeof initialState === 'undefined') {
-      sanityError = new Error(
-        `Reducer "${key}" returned undefined during initialization. ` +
-        `If the state passed to the reducer is undefined, you must ` +
-        `explicitly return the initial state. The initial state may ` +
-        `not be undefined.`
-      );
-    }
-
-    var type = '@@redux/PROBE_UNKNOWN_ACTION_' + Math.random().toString(36).substring(7).split('').join('.');
-    if (!sanityError && typeof reducer(undefined, { type }) === 'undefined') {
-      sanityError = new Error(
-        `Reducer "${key}" returned undefined when probed with a random type. ` +
-        `Don't try to handle ${ActionTypes.INIT} or other actions in "redux/*" ` +
-        `namespace. They are considered private. Instead, you must return the ` +
-        `current state for any unknown actions, unless it is undefined, ` +
-        `in which case you must return the initial state, regardless of the ` +
-        `action type. The initial state may not be undefined.`
-      );
-    }
-  });
+  try {
+    assertReducerSanity(finalReducers);
+  } catch (e) {
+    sanityError = e;
+  }
 
   var defaultState = mapValues(finalReducers, () => undefined);
 
@@ -112,16 +112,21 @@ export default function combineReducers(reducers) {
     if (sanityError) {
       throw sanityError;
     }
+
     var finalState = mapValues(finalReducers, (reducer, key) => {
       var newState = reducer(state[key], action);
       if (typeof newState === 'undefined') {
-        throw new Error(getErrorMessage(key, action));
+        var errorMessage = getUndefinedStateErrorMessage(key, action);
+        throw new Error(errorMessage);
       }
       return newState;
     });
 
     if (process.env.NODE_ENV !== 'production') {
-      verifyStateShape(state, finalState, action);
+      var warningMessage = getUnexpectedStateKeyWarningMessage(state, finalState, action);
+      if (warningMessage) {
+        console.error(warningMessage);
+      }
     }
 
     return finalState;