diff --git a/java/src/com/android/inputmethod/latin/DictionaryFacilitator.java b/java/src/com/android/inputmethod/latin/DictionaryFacilitator.java
index ff798ab..9d8bdb2 100644
--- a/java/src/com/android/inputmethod/latin/DictionaryFacilitator.java
+++ b/java/src/com/android/inputmethod/latin/DictionaryFacilitator.java
@@ -17,6 +17,7 @@
 package com.android.inputmethod.latin;
 
 import android.content.Context;
+import android.util.LruCache;
 
 import com.android.inputmethod.annotations.UsedForTesting;
 import com.android.inputmethod.keyboard.Keyboard;
@@ -55,6 +56,18 @@
             Dictionary.TYPE_USER};
 
     /**
+     * The facilitator will put words into the cache whenever it decodes them.
+     * @param cache
+     */
+    void setValidSpellingWordReadCache(final LruCache<String, Boolean> cache);
+
+    /**
+     * The facilitator will get words from the cache whenever it needs to check their spelling.
+     * @param cache
+     */
+    void setValidSpellingWordWriteCache(final LruCache<String, Boolean> cache);
+
+    /**
      * Returns whether this facilitator is exactly for this locale.
      *
      * @param locale the locale to test against
diff --git a/java/src/com/android/inputmethod/latin/DictionaryFacilitatorImpl.java b/java/src/com/android/inputmethod/latin/DictionaryFacilitatorImpl.java
index 7233d27..6508eb2 100644
--- a/java/src/com/android/inputmethod/latin/DictionaryFacilitatorImpl.java
+++ b/java/src/com/android/inputmethod/latin/DictionaryFacilitatorImpl.java
@@ -19,6 +19,7 @@
 import android.content.Context;
 import android.text.TextUtils;
 import android.util.Log;
+import android.util.LruCache;
 
 import com.android.inputmethod.annotations.UsedForTesting;
 import com.android.inputmethod.keyboard.Keyboard;
@@ -82,6 +83,19 @@
     private static final Class<?>[] DICT_FACTORY_METHOD_ARG_TYPES =
             new Class[] { Context.class, Locale.class, File.class, String.class, String.class };
 
+    private LruCache<String, Boolean> mValidSpellingWordReadCache;
+    private LruCache<String, Boolean> mValidSpellingWordWriteCache;
+
+    @Override
+    public void setValidSpellingWordReadCache(final LruCache<String, Boolean> cache) {
+        mValidSpellingWordReadCache = cache;
+    }
+
+    @Override
+    public void setValidSpellingWordWriteCache(final LruCache<String, Boolean> cache) {
+        mValidSpellingWordWriteCache = cache;
+    }
+
     @Override
     public boolean isForLocale(final Locale locale) {
         return locale != null && locale.equals(mDictionaryGroup.mLocale);
@@ -341,6 +355,10 @@
                 dictionarySetToCleanup.closeDict(dictType);
             }
         }
+
+        if (mValidSpellingWordWriteCache != null) {
+            mValidSpellingWordWriteCache.evictAll();
+        }
     }
 
     private void asyncReloadUninitializedMainDictionaries(final Context context,
@@ -464,6 +482,10 @@
     public void addToUserHistory(final String suggestion, final boolean wasAutoCapitalized,
             @Nonnull final NgramContext ngramContext, final long timeStampInSeconds,
             final boolean blockPotentiallyOffensive) {
+        // Update the spelling cache before learning. Words that are not yet added to user history
+        // and appear in no other language model are not considered valid.
+        putWordIntoValidSpellingWordCache("addToUserHistory", suggestion);
+
         final String[] words = suggestion.split(Constants.WORD_SEPARATOR);
         NgramContext ngramContextForCurrentWord = ngramContext;
         for (int i = 0; i < words.length; i++) {
@@ -477,6 +499,12 @@
         }
     }
 
+    private void putWordIntoValidSpellingWordCache(final String caller, final String word) {
+        final String spellingWord = word.toLowerCase(getLocale());
+        final boolean isValid = isValidSpellingWord(spellingWord);
+        mValidSpellingWordWriteCache.put(spellingWord, isValid);
+    }
+
     private void addWordToUserHistory(final DictionaryGroup dictionaryGroup,
             final NgramContext ngramContext, final String word, final boolean wasAutoCapitalized,
             final int timeStampInSeconds, final boolean blockPotentiallyOffensive) {
@@ -543,6 +571,10 @@
         if (eventType != Constants.EVENT_BACKSPACE) {
             removeWord(Dictionary.TYPE_USER_HISTORY, word);
         }
+
+        // Update the spelling cache after unlearning. Words that are removed from user history
+        // and appear in no other language model are not considered valid.
+        putWordIntoValidSpellingWordCache("unlearnFromUserHistory", word.toLowerCase());
     }
 
     // TODO: Revise the way to fusion suggestion results.
@@ -577,6 +609,14 @@
     }
 
     public boolean isValidSpellingWord(final String word) {
+        if (mValidSpellingWordReadCache != null) {
+            final String spellingWord = word.toLowerCase(getLocale());
+            final Boolean cachedValue = mValidSpellingWordReadCache.get(spellingWord);
+            if (cachedValue != null) {
+                return cachedValue;
+            }
+        }
+
         return isValidWord(word, ALL_DICTIONARY_TYPES);
     }
 
diff --git a/java/src/com/android/inputmethod/latin/spellcheck/AndroidSpellCheckerSession.java b/java/src/com/android/inputmethod/latin/spellcheck/AndroidSpellCheckerSession.java
index 2c690ae..c7622e7 100644
--- a/java/src/com/android/inputmethod/latin/spellcheck/AndroidSpellCheckerSession.java
+++ b/java/src/com/android/inputmethod/latin/spellcheck/AndroidSpellCheckerSession.java
@@ -84,8 +84,7 @@
                 if (TextUtils.isEmpty(splitText)) {
                     continue;
                 }
-                if (mSuggestionsCache.getSuggestionsFromCache(splitText.toString(), ngramContext)
-                        == null) {
+                if (mSuggestionsCache.getSuggestionsFromCache(splitText.toString()) == null) {
                     continue;
                 }
                 final int newLength = splitText.length();
diff --git a/java/src/com/android/inputmethod/latin/spellcheck/AndroidWordLevelSpellCheckerSession.java b/java/src/com/android/inputmethod/latin/spellcheck/AndroidWordLevelSpellCheckerSession.java
index 1322ce2..9223923 100644
--- a/java/src/com/android/inputmethod/latin/spellcheck/AndroidWordLevelSpellCheckerSession.java
+++ b/java/src/com/android/inputmethod/latin/spellcheck/AndroidWordLevelSpellCheckerSession.java
@@ -71,30 +71,26 @@
     }
 
     protected static final class SuggestionsCache {
-        private static final char CHAR_DELIMITER = '\uFFFC';
         private static final int MAX_CACHE_SIZE = 50;
         private final LruCache<String, SuggestionsParams> mUnigramSuggestionsInfoCache =
                 new LruCache<>(MAX_CACHE_SIZE);
 
-        private static String generateKey(final String query, final NgramContext ngramContext) {
-            if (TextUtils.isEmpty(query) || !ngramContext.isValid()) {
-                return query;
-            }
-            return query + CHAR_DELIMITER + ngramContext;
+        private static String generateKey(final String query) {
+            return query + "";
         }
 
-        public SuggestionsParams getSuggestionsFromCache(String query,
-                final NgramContext ngramContext) {
-            return mUnigramSuggestionsInfoCache.get(generateKey(query, ngramContext));
+        public SuggestionsParams getSuggestionsFromCache(final String query) {
+            return mUnigramSuggestionsInfoCache.get(query);
         }
 
-        public void putSuggestionsToCache(final String query, final NgramContext ngramContext,
-                final String[] suggestions, final int flags) {
+        public void putSuggestionsToCache(
+                final String query, final String[] suggestions, final int flags) {
             if (suggestions == null || TextUtils.isEmpty(query)) {
                 return;
             }
             mUnigramSuggestionsInfoCache.put(
-                    generateKey(query, ngramContext), new SuggestionsParams(suggestions, flags));
+                    generateKey(query),
+                    new SuggestionsParams(suggestions, flags));
         }
 
         public void clearCache() {
@@ -232,16 +228,7 @@
                             AndroidSpellCheckerService.SINGLE_QUOTE).
                     replaceAll("^" + quotesRegexp, "").
                     replaceAll(quotesRegexp + "$", "");
-            final SuggestionsParams cachedSuggestionsParams =
-                    mSuggestionsCache.getSuggestionsFromCache(text, ngramContext);
 
-            if (cachedSuggestionsParams != null) {
-                Log.d(TAG, "onGetSuggestionsInternal() : Cache hit for [" + text + "]");
-                return new SuggestionsInfo(
-                        cachedSuggestionsParams.mFlags, cachedSuggestionsParams.mSuggestions);
-            }
-
-            // If spell checking is impossible, return early.
             if (!mService.hasMainDictionaryForLocale(mLocale)) {
                 return AndroidSpellCheckerService.getNotInDictEmptySuggestions(
                         false /* reportAsTypo */);
@@ -329,8 +316,7 @@
                                     .getValueOf_RESULT_ATTR_HAS_RECOMMENDED_SUGGESTIONS()
                             : 0);
             final SuggestionsInfo retval = new SuggestionsInfo(flags, result.mSuggestions);
-            mSuggestionsCache.putSuggestionsToCache(text, ngramContext, result.mSuggestions,
-                    flags);
+            mSuggestionsCache.putSuggestionsToCache(text, result.mSuggestions, flags);
             return retval;
         } catch (RuntimeException e) {
             // Don't kill the keyboard if there is a bug in the spell checker