diff --git a/user/super/com/google/gwt/emul/java/io/Writer.java b/user/super/com/google/gwt/emul/java/io/Writer.java
index a2e34e2..d837120 100644
--- a/user/super/com/google/gwt/emul/java/io/Writer.java
+++ b/user/super/com/google/gwt/emul/java/io/Writer.java
@@ -15,7 +15,6 @@
  */
 package java.io;
 
-import static javaemul.internal.InternalPreconditions.checkCriticalStringBounds;
 import static javaemul.internal.InternalPreconditions.checkNotNull;
 
 import java.util.Objects;
@@ -76,15 +75,6 @@
     if (csq == null) {
       csq = "null";
     }
-    /*
-     * Ensure we throw StringIndexOutOfBoundsException as String#subsequence method depends on
-     * JavaScript's string#substr() which has different behaviour than original Java method.
-     *
-     * JavaScript behaviour of substr(start, length):
-     * "gwt".substr(0, -1) returns ""
-     * "gwt".substr(-1, 1) returns "t" -> Calculates substring from end.
-     */
-    checkCriticalStringBounds(start, end, csq.length());
     write(csq.subSequence(start, end).toString());
     return this;
   }
diff --git a/user/super/com/google/gwt/emul/java/lang/AbstractStringBuilder.java b/user/super/com/google/gwt/emul/java/lang/AbstractStringBuilder.java
index dabfd83..159dbde 100644
--- a/user/super/com/google/gwt/emul/java/lang/AbstractStringBuilder.java
+++ b/user/super/com/google/gwt/emul/java/lang/AbstractStringBuilder.java
@@ -15,6 +15,8 @@
  */
 package java.lang;
 
+import static javaemul.internal.InternalPreconditions.checkStringElementIndex;
+
 /**
  * A base class to share implementation between {@link StringBuffer} and {@link StringBuilder}.
  * <p>
@@ -113,6 +115,14 @@
   }
 
   void replace0(int start, int end, String toInsert) {
+    int length = string.length();
+    if (end > length) {
+      end = length;
+    } else {
+      // Only checking for start > end; since rest is checked with substring.
+      checkStringElementIndex(start, end + 1);
+    }
+
     string = string.substring(0, start) + toInsert + string.substring(end);
   }
 
@@ -142,4 +152,4 @@
     buffer[f] = buffer[s];
     buffer[s] = tmp;
   }
-}
\ No newline at end of file
+}
diff --git a/user/super/com/google/gwt/emul/java/lang/String.java b/user/super/com/google/gwt/emul/java/lang/String.java
index 0b58db7..45ddd0e 100644
--- a/user/super/com/google/gwt/emul/java/lang/String.java
+++ b/user/super/com/google/gwt/emul/java/lang/String.java
@@ -18,6 +18,7 @@
 
 import static javaemul.internal.InternalPreconditions.checkCriticalStringBounds;
 import static javaemul.internal.InternalPreconditions.checkNotNull;
+import static javaemul.internal.InternalPreconditions.checkStringBounds;
 import static javaemul.internal.InternalPreconditions.checkStringElementIndex;
 
 import java.io.Serializable;
@@ -27,14 +28,12 @@
 import java.util.Comparator;
 import java.util.Locale;
 import java.util.StringJoiner;
-
 import javaemul.internal.ArrayHelper;
 import javaemul.internal.EmulatedCharset;
 import javaemul.internal.HashCodes;
 import javaemul.internal.JsUtils;
 import javaemul.internal.NativeRegExp;
 import javaemul.internal.annotations.DoNotInline;
-
 import jsinterop.annotations.JsMethod;
 import jsinterop.annotations.JsNonNull;
 import jsinterop.annotations.JsPackage;
@@ -560,7 +559,8 @@
     // treat "$$" as "$".
 
     // Escape regex special characters from literal replacement string.
-    String regex = from.toString().replaceAll("([/\\\\\\.\\*\\+\\?\\|\\(\\)\\[\\]\\{\\}$^])", "\\\\$1");
+    String regex =
+        from.toString().replaceAll("([/\\\\\\.\\*\\+\\?\\|\\(\\)\\[\\]\\{\\}$^])", "\\\\$1");
     // Escape $ since it is for match backrefs and \ since it is used to escape
     // $.
     String replacement = to.toString().replaceAll("\\\\", "\\\\\\\\").replaceAll("\\$", "\\\\$");
@@ -682,10 +682,12 @@
   }
 
   public String substring(int beginIndex) {
+    checkStringElementIndex(beginIndex, length() + 1);
     return asNativeString().substr(beginIndex);
   }
 
   public String substring(int beginIndex, int endIndex) {
+    checkStringBounds(beginIndex, endIndex, length());
     return asNativeString().substr(beginIndex, endIndex - beginIndex);
   }
 
@@ -732,10 +734,6 @@
 
   @Override
   public String toString() {
-    /*
-     * Magic: this method is only used during compiler optimizations; the generated JS will instead alias
-     * this method to the native String.prototype.toString() function.
-     */
     return checkNotNull(this);
   }
 
diff --git a/user/super/com/google/gwt/emul/javaemul/internal/InternalPreconditions.java b/user/super/com/google/gwt/emul/javaemul/internal/InternalPreconditions.java
index a427e59..a66c330 100644
--- a/user/super/com/google/gwt/emul/javaemul/internal/InternalPreconditions.java
+++ b/user/super/com/google/gwt/emul/javaemul/internal/InternalPreconditions.java
@@ -591,6 +591,23 @@
    *
    * @throws StringIndexOutOfBoundsException if the range is not legal
    */
+  public static void checkStringBounds(int start, int end, int length) {
+    if (IS_BOUNDS_CHECKED) {
+      checkCriticalStringBounds(start, end, length);
+    } else if (IS_ASSERTED) {
+      try {
+        checkCriticalStringBounds(start, end, length);
+      } catch (Exception e) {
+        throw new AssertionError(e);
+      }
+    }
+  }
+
+  /**
+   * Checks that string bounds are correct.
+   *
+   * @throws StringIndexOutOfBoundsException if the range is not legal
+   */
   public static void checkCriticalStringBounds(int start, int end, int length) {
     if (start < 0 || end > length || end < start) {
       throw new StringIndexOutOfBoundsException(
diff --git a/user/test/com/google/gwt/emultest/java/lang/StringTest.java b/user/test/com/google/gwt/emultest/java/lang/StringTest.java
index e940b92..4791200 100644
--- a/user/test/com/google/gwt/emultest/java/lang/StringTest.java
+++ b/user/test/com/google/gwt/emultest/java/lang/StringTest.java
@@ -811,6 +811,32 @@
     assertEquals("cd", hideFromCompiler("abcdefghi").substring(2, 4));
     assertEquals("bc", hideFromCompiler("abcdef").substring(1, 3));
     assertEquals("bcdef", hideFromCompiler("abcdef").substring(1));
+    assertEquals("", hideFromCompiler("abcdef").substring(6));
+    assertEquals("", hideFromCompiler("abcdef").substring(6, 6));
+
+    try {
+      hideFromCompiler("abc").substring(-1);
+      fail("Should have thrown");
+    } catch (IndexOutOfBoundsException expected) {
+    }
+
+    try {
+      hideFromCompiler("abc").substring(4);
+      fail("Should have thrown");
+    } catch (IndexOutOfBoundsException expected) {
+    }
+
+    try {
+      hideFromCompiler("abc").substring(2, 4);
+      fail("Should have thrown");
+    } catch (IndexOutOfBoundsException expected) {
+    }
+
+    try {
+      hideFromCompiler("abc").substring(2, 1);
+      fail("Should have thrown");
+    } catch (IndexOutOfBoundsException expected) {
+    }
   }
 
   public void testToCharArray() {