diff --git a/java/src/com/android/inputmethod/dictionarypack/LocaleUtils.java b/java/src/com/android/inputmethod/dictionarypack/LocaleUtils.java
index d0e8446..77f67b8 100644
--- a/java/src/com/android/inputmethod/dictionarypack/LocaleUtils.java
+++ b/java/src/com/android/inputmethod/dictionarypack/LocaleUtils.java
@@ -144,7 +144,7 @@
     public static String getMatchLevelSortedString(final int matchLevel) {
         // This works because the match levels are 0~99 (actually 0~30)
         // Ideally this should use a number of digits equals to the 1og10 of the greater matchLevel
-        return String.format("%02d", MATCH_LEVEL_MAX - matchLevel);
+        return String.format(Locale.ROOT, "%02d", MATCH_LEVEL_MAX - matchLevel);
     }
 
     /**
diff --git a/java/src/com/android/inputmethod/keyboard/Key.java b/java/src/com/android/inputmethod/keyboard/Key.java
index 1550e77..ae72b4a 100644
--- a/java/src/com/android/inputmethod/keyboard/Key.java
+++ b/java/src/com/android/inputmethod/keyboard/Key.java
@@ -453,7 +453,7 @@
         } else {
             label = "/" + mLabel;
         }
-        return String.format("%s%s %d,%d %dx%d %s/%s/%s",
+        return String.format(Locale.ROOT, "%s%s %d,%d %dx%d %s/%s/%s",
                 Constants.printableCode(mCode), label, mX, mY, mWidth, mHeight, mHintLabel,
                 KeyboardIconsSet.getIconName(mIconId), backgroundName(mBackgroundType));
     }
diff --git a/java/src/com/android/inputmethod/keyboard/KeyboardId.java b/java/src/com/android/inputmethod/keyboard/KeyboardId.java
index aa27067..4c5dd25 100644
--- a/java/src/com/android/inputmethod/keyboard/KeyboardId.java
+++ b/java/src/com/android/inputmethod/keyboard/KeyboardId.java
@@ -187,7 +187,7 @@
     public String toString() {
         final String orientation = (mOrientation == Configuration.ORIENTATION_PORTRAIT)
                 ? "port" : "land";
-        return String.format("[%s %s:%s %s:%dx%d %s %s %s%s%s%s%s%s%s%s%s]",
+        return String.format(Locale.ROOT, "[%s %s:%s %s:%dx%d %s %s %s%s%s%s%s%s%s%s%s]",
                 elementIdToName(mElementId),
                 mLocale,
                 mSubtype.getExtraValueOf(KEYBOARD_LAYOUT_SET),
diff --git a/java/src/com/android/inputmethod/latin/LocaleUtils.java b/java/src/com/android/inputmethod/latin/LocaleUtils.java
index 5fde815..a1e4050 100644
--- a/java/src/com/android/inputmethod/latin/LocaleUtils.java
+++ b/java/src/com/android/inputmethod/latin/LocaleUtils.java
@@ -148,7 +148,7 @@
     public static String getMatchLevelSortedString(int matchLevel) {
         // This works because the match levels are 0~99 (actually 0~30)
         // Ideally this should use a number of digits equals to the 1og10 of the greater matchLevel
-        return String.format("%02d", MATCH_LEVEL_MAX - matchLevel);
+        return String.format(Locale.ROOT, "%02d", MATCH_LEVEL_MAX - matchLevel);
     }
 
     /**
diff --git a/java/src/com/android/inputmethod/latin/Suggest.java b/java/src/com/android/inputmethod/latin/Suggest.java
index 2d1141b..1ad040d 100644
--- a/java/src/com/android/inputmethod/latin/Suggest.java
+++ b/java/src/com/android/inputmethod/latin/Suggest.java
@@ -379,7 +379,8 @@
                     typedWord, cur.toString(), cur.mScore);
             final String scoreInfoString;
             if (normalizedScore > 0) {
-                scoreInfoString = String.format("%d (%4.2f)", cur.mScore, normalizedScore);
+                scoreInfoString = String.format(
+                        Locale.ROOT, "%d (%4.2f)", cur.mScore, normalizedScore);
             } else {
                 scoreInfoString = Integer.toString(cur.mScore);
             }
diff --git a/tests/src/com/android/inputmethod/keyboard/internal/KeySpecParserTests.java b/tests/src/com/android/inputmethod/keyboard/internal/KeySpecParserTests.java
index b1ae6f5..861abe8 100644
--- a/tests/src/com/android/inputmethod/keyboard/internal/KeySpecParserTests.java
+++ b/tests/src/com/android/inputmethod/keyboard/internal/KeySpecParserTests.java
@@ -35,8 +35,8 @@
 
     private static final String CODE_SETTINGS = "!code/key_settings";
     private static final String ICON_SETTINGS = "!icon/settings_key";
-    private static final String CODE_SETTINGS_UPPERCASE = CODE_SETTINGS.toUpperCase();
-    private static final String ICON_SETTINGS_UPPERCASE = ICON_SETTINGS.toUpperCase();
+    private static final String CODE_SETTINGS_UPPERCASE = CODE_SETTINGS.toUpperCase(Locale.ROOT);
+    private static final String ICON_SETTINGS_UPPERCASE = ICON_SETTINGS.toUpperCase(Locale.ROOT);
     private static final String CODE_NON_EXISTING = "!code/non_existing";
     private static final String ICON_NON_EXISTING = "!icon/non_existing";
 
@@ -587,7 +587,7 @@
                 new String[] { null, "a", "b", "c" }, true);
         // Upper case specification will not work.
         assertGetBooleanValue("HAS LABEL", HAS_LABEL,
-                new String[] { HAS_LABEL.toUpperCase(), "a", "b", "c" },
+                new String[] { HAS_LABEL.toUpperCase(Locale.ROOT), "a", "b", "c" },
                 new String[] { "!HASLABEL!", "a", "b", "c" }, false);
 
         assertGetBooleanValue("No has label", HAS_LABEL,
@@ -600,13 +600,13 @@
         // Upper case specification will not work.
         assertGetBooleanValue("Multiple has label", HAS_LABEL,
                 new String[] {
-                    "a", HAS_LABEL.toUpperCase(), "b", "c", HAS_LABEL, "d" },
+                    "a", HAS_LABEL.toUpperCase(Locale.ROOT), "b", "c", HAS_LABEL, "d" },
                 new String[] {
                     "a", "!HASLABEL!", "b", "c", null, "d" }, true);
         // Upper case specification will not work.
         assertGetBooleanValue("Multiple has label with needs dividers", HAS_LABEL,
                 new String[] {
-                    "a", HAS_LABEL, "b", NEEDS_DIVIDER, HAS_LABEL.toUpperCase(), "d" },
+                    "a", HAS_LABEL, "b", NEEDS_DIVIDER, HAS_LABEL.toUpperCase(Locale.ROOT), "d" },
                 new String[] {
                     "a", null, "b", NEEDS_DIVIDER, "!HASLABEL!", "d" }, true);
     }
@@ -625,7 +625,7 @@
                 new String[] { null, "a", "b", "c" }, 3);
         // Upper case specification will not work.
         assertGetIntValue("FIXED COLUMN ORDER 3", FIXED_COLUMN_ORDER, -1,
-                new String[] { FIXED_COLUMN_ORDER.toUpperCase() + "3", "a", "b", "c" },
+                new String[] { FIXED_COLUMN_ORDER.toUpperCase(Locale.ROOT) + "3", "a", "b", "c" },
                 new String[] { "!FIXEDCOLUMNORDER!3", "a", "b", "c" }, -1);
 
         assertGetIntValue("No fixed column order", FIXED_COLUMN_ORDER, -1,
@@ -641,7 +641,7 @@
         // Upper case specification will not work.
         assertGetIntValue("Multiple fixed column order 5,3 with has label", FIXED_COLUMN_ORDER, -1,
                 new String[] {
-                    FIXED_COLUMN_ORDER.toUpperCase() + "5", HAS_LABEL, "a",
+                    FIXED_COLUMN_ORDER.toUpperCase(Locale.ROOT) + "5", HAS_LABEL, "a",
                     FIXED_COLUMN_ORDER + "3", "b" },
                 new String[] { "!FIXEDCOLUMNORDER!5", HAS_LABEL, "a", null, "b" }, 3);
     }