diff --git a/teavm-classlib/src/main/java/org/teavm/classlib/impl/unicode/UnicodeSupport.java b/teavm-classlib/src/main/java/org/teavm/classlib/impl/unicode/UnicodeSupport.java
index 225d6d2ae..296b99b0c 100644
--- a/teavm-classlib/src/main/java/org/teavm/classlib/impl/unicode/UnicodeSupport.java
+++ b/teavm-classlib/src/main/java/org/teavm/classlib/impl/unicode/UnicodeSupport.java
@@ -144,12 +144,12 @@ public class UnicodeSupport {
         int j = 0;
         int t = 0;
         while (true) {
-            if (i == a.length) {
+            if (j == b.length) {
                 while (i < a.length) {
                     result[t++] = a[i++];
                 }
                 break;
-            } else if (j == b.length) {
+            } else if (i == a.length) {
                 while (j < b.length) {
                     result[t++] = b[j++];
                 }
diff --git a/teavm-classlib/src/test/java/org/teavm/classlib/impl/unicode/UnicodeSupportTest.java b/teavm-classlib/src/test/java/org/teavm/classlib/impl/unicode/UnicodeSupportTest.java
new file mode 100644
index 000000000..802e0e123
--- /dev/null
+++ b/teavm-classlib/src/test/java/org/teavm/classlib/impl/unicode/UnicodeSupportTest.java
@@ -0,0 +1,20 @@
+package org.teavm.classlib.impl.unicode;
+
+import static org.junit.Assert.assertFalse;
+
+public class UnicodeSupportTest {
+
+    private static boolean pairsEqual(final int[] pairs, final int index1, final int index2) {
+        return pairs[index1] == pairs[index2] && pairs[index1 + 1] == pairs[index2 + 1];
+    }
+
+    @Test
+    public void test_getDigitValues() {
+        final int[] digitValues = UnicodeSupport.getDigitValues();
+        if (digitValues.length >= 4) {
+            // there are no duplicates, so the last two pairs should not be identical
+            assertFalse(pairsEqual(digitValues, digitValues.length - 4, digitValues.length - 2));
+        }
+    }
+
+}