diff --git a/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TAbstractStringBuilder.java b/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TAbstractStringBuilder.java
index fdd03076b..1d2f664ca 100644
--- a/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TAbstractStringBuilder.java
+++ b/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TAbstractStringBuilder.java
@@ -115,7 +115,7 @@ class TAbstractStringBuilder extends TObject implements TSerializable, TCharSequ
             } else {
                 insertSpace(target, target + 1);
             }
-            buffer[target++] = (char)('0' + value);
+            buffer[target++] = TCharacter.forDigit(value, radix);
         } else {
             int pos = 1;
             int sz = 1;
diff --git a/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TMath.java b/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TMath.java
index b64d4305b..dcbc6cefb 100644
--- a/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TMath.java
+++ b/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TMath.java
@@ -93,11 +93,11 @@ public final class TMath extends TObject {
     public static native double atan2(double y, double x);
 
     public static int round(float a) {
-        return (int)(a + 0.5f);
+        return (int)(a + signum(a) * 0.5f);
     }
 
     public static long round(double a) {
-        return (long)(a + 0.5);
+        return (long)(a + signum(a) * 0.5);
     }
 
     @GeneratedBy(MathNativeGenerator.class)
diff --git a/teavm-classlib/src/main/java/org/teavm/classlib/java/util/TCollections.java b/teavm-classlib/src/main/java/org/teavm/classlib/java/util/TCollections.java
index 6816aea8e..b9417c35f 100644
--- a/teavm-classlib/src/main/java/org/teavm/classlib/java/util/TCollections.java
+++ b/teavm-classlib/src/main/java/org/teavm/classlib/java/util/TCollections.java
@@ -253,6 +253,9 @@ public class TCollections extends TObject {
         }
         int l = 0;
         int u = list.size() - 1;
+        if (u < 0) {
+            return -1;
+        }
         while (true) {
             int i = (l + u) / 2;
             T e = list.get(i);
diff --git a/teavm-tests/src/test/java/org/teavm/classlib/java/lang/IntegerTest.java b/teavm-tests/src/test/java/org/teavm/classlib/java/lang/IntegerTest.java
index 485663cf2..d0f84f2ba 100644
--- a/teavm-tests/src/test/java/org/teavm/classlib/java/lang/IntegerTest.java
+++ b/teavm-tests/src/test/java/org/teavm/classlib/java/lang/IntegerTest.java
@@ -58,6 +58,11 @@ public class IntegerTest {
         assertEquals("kona", Integer.toString(411787, 27));
     }
 
+    @Test
+    public void writesSingleDigitInteger() {
+        assertEquals("a", Integer.toString(10, 16));
+    }
+
     @Test
     public void decodes() {
         assertEquals(Integer.valueOf(123), Integer.decode("123"));
diff --git a/teavm-tests/src/test/java/org/teavm/classlib/java/lang/MathTest.java b/teavm-tests/src/test/java/org/teavm/classlib/java/lang/MathTest.java
index 471523b8c..58249bcb9 100644
--- a/teavm-tests/src/test/java/org/teavm/classlib/java/lang/MathTest.java
+++ b/teavm-tests/src/test/java/org/teavm/classlib/java/lang/MathTest.java
@@ -54,4 +54,12 @@ public class MathTest {
     public void getExponentComputed() {
         assertEquals(6, Math.getExponent(123.456));
     }
+
+    @Test
+    public void roundWorks() {
+        assertEquals(1, Math.round(1.3));
+        assertEquals(2, Math.round(1.8));
+        assertEquals(-1, Math.round(-1.3));
+        assertEquals(-2, Math.round(-1.8));
+    }
 }