diff --git a/src/main/java/com/google/gwtorm/schema/sql/DialectH2.java b/src/main/java/com/google/gwtorm/schema/sql/DialectH2.java
index af061f0..3cf7ff9 100644
--- a/src/main/java/com/google/gwtorm/schema/sql/DialectH2.java
+++ b/src/main/java/com/google/gwtorm/schema/sql/DialectH2.java
@@ -38,9 +38,9 @@
       final SQLException err) {
     switch (getSQLStateInt(err)) {
       case 23001: // UNIQUE CONSTRAINT VIOLATION
+      case 23505: // DUPLICATE_KEY_1
         return new OrmDuplicateKeyException(entity, err);
 
-      case 23000: // CHECK CONSTRAINT VIOLATION
       default:
         return super.convertError(op, entity, err);
     }
diff --git a/src/main/java/com/google/gwtorm/schema/sql/DialectMySQL.java b/src/main/java/com/google/gwtorm/schema/sql/DialectMySQL.java
index e07740d..aad5037 100644
--- a/src/main/java/com/google/gwtorm/schema/sql/DialectMySQL.java
+++ b/src/main/java/com/google/gwtorm/schema/sql/DialectMySQL.java
@@ -17,6 +17,7 @@
 import com.google.gwtorm.client.Column;
 import com.google.gwtorm.schema.ColumnModel;
 import com.google.gwtorm.schema.SequenceModel;
+import com.google.gwtorm.server.OrmDuplicateKeyException;
 import com.google.gwtorm.server.OrmException;
 import com.google.gwtorm.server.StatementExecutor;
 
@@ -214,4 +215,16 @@
     r.append(getSqlTypeInfo(col).getSqlType(col, this));
     stmt.execute(r.toString());
   }
+
+  @Override
+  public OrmException convertError(String op, String entity, SQLException err) {
+    switch (err.getErrorCode()) {
+      case 1022: // ER_DUP_KEY
+      case 1062: // ER_DUP_ENTRY
+      case 1169: // ER_DUP_UNIQUE;
+        return new OrmDuplicateKeyException(entity, err);
+      default:
+        return super.convertError(op, entity, err);
+    }
+  }
 }
diff --git a/src/main/java/com/google/gwtorm/schema/sql/DialectOracle.java b/src/main/java/com/google/gwtorm/schema/sql/DialectOracle.java
index 827c656..d006b16 100644
--- a/src/main/java/com/google/gwtorm/schema/sql/DialectOracle.java
+++ b/src/main/java/com/google/gwtorm/schema/sql/DialectOracle.java
@@ -15,6 +15,7 @@
 package com.google.gwtorm.schema.sql;
 
 import com.google.gwtorm.schema.ColumnModel;
+import com.google.gwtorm.server.OrmDuplicateKeyException;
 import com.google.gwtorm.server.OrmException;
 import com.google.gwtorm.server.StatementExecutor;
 
@@ -148,4 +149,14 @@
   public boolean isStatementDelimiterSupported() {
     return false;
   }
+
+  @Override
+  public OrmException convertError(String op, String entity, SQLException err) {
+    switch (err.getErrorCode()) {
+      case 1: // ORA-00001: unique constraint violated
+        return new OrmDuplicateKeyException(entity, err);
+      default:
+        return super.convertError(op, entity, err);
+    }
+  }
 }
diff --git a/src/test/java/com/google/gwtorm/schema/sql/SqlDialectTest.java b/src/test/java/com/google/gwtorm/schema/sql/SqlDialectTest.java
index ac8cd46..b159b83 100644
--- a/src/test/java/com/google/gwtorm/schema/sql/SqlDialectTest.java
+++ b/src/test/java/com/google/gwtorm/schema/sql/SqlDialectTest.java
@@ -15,12 +15,17 @@
 package com.google.gwtorm.schema.sql;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 
 import com.google.gwtorm.data.Person;
 import com.google.gwtorm.data.PhoneBookDb;
 import com.google.gwtorm.data.PhoneBookDb2;
 import com.google.gwtorm.jdbc.Database;
 import com.google.gwtorm.jdbc.JdbcExecutor;
+import com.google.gwtorm.server.OrmDuplicateKeyException;
 import com.google.gwtorm.server.OrmException;
 
 import org.junit.Test;
@@ -29,6 +34,7 @@
 import java.sql.SQLException;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Collections;
 
 public abstract class SqlDialectTest {
   protected JdbcExecutor executor;
@@ -75,4 +81,51 @@
     List<Person> r = schema.people().olderThan(10).toList();
     assertEquals(1, r.size());
   }
+
+  @Test
+  public void testThrowsOrmDuplicateKeyExceptionWhenTryingToInsertDuplicates()
+      throws Exception {
+    PhoneBookDb p = phoneBook.open();
+    try {
+      p.updateSchema(executor);
+
+      final Person.Key pk = new Person.Key("Bob");
+      final Person bob = new Person(pk, 18);
+      p.people().insert(Collections.singleton(bob));
+
+      p.people().insert(Collections.singleton(bob));
+      fail("Expected " + OrmDuplicateKeyException.class);
+    } catch (OrmDuplicateKeyException e) {
+      assertTrue(e.getCause() instanceof SQLException);
+      assertContainsString(e.getMessage(), p.people().getRelationName());
+    } finally {
+      p.close();
+    }
+  }
+
+  @Test
+  public void testThrowsOrmExceptionForOtherErrors() throws Exception {
+    PhoneBookDb p = phoneBook.open();
+    try {
+      p.updateSchema(executor);
+
+      String invalidKey = null;
+      final Person.Key pk = new Person.Key(invalidKey);
+      final Person bob = new Person(pk, 18);
+
+      p.people().insert(Collections.singleton(bob));
+      fail("Expected " + OrmException.class);
+    } catch (OrmException e) {
+      assertTrue(e.getCause() instanceof SQLException);
+      assertFalse(e instanceof OrmDuplicateKeyException);
+      assertContainsString(e.getMessage(), p.people().getRelationName());
+    } finally {
+      p.close();
+    }
+  }
+
+  private void assertContainsString(String string, String substring) {
+    assertNotNull(string);
+    assertTrue(string.contains(substring));
+  }
 }