diff --git a/spring-jdbc/src/main/java/org/springframework/jdbc/datasource/LazyConnectionDataSourceProxy.java b/spring-jdbc/src/main/java/org/springframework/jdbc/datasource/LazyConnectionDataSourceProxy.java
index 3244f01e1940..ed352bf38857 100644
--- a/spring-jdbc/src/main/java/org/springframework/jdbc/datasource/LazyConnectionDataSourceProxy.java
+++ b/spring-jdbc/src/main/java/org/springframework/jdbc/datasource/LazyConnectionDataSourceProxy.java
@@ -163,6 +163,8 @@ public void setDefaultTransactionIsolationName(String constantName) {
 	 * @see java.sql.Connection#setTransactionIsolation
 	 */
 	public void setDefaultTransactionIsolation(int defaultTransactionIsolation) {
+		Assert.isTrue(constants.containsValue(defaultTransactionIsolation),
+				"Only values of transaction isolation constants allowed");
 		this.defaultTransactionIsolation = defaultTransactionIsolation;
 	}
 
diff --git a/spring-jdbc/src/test/java/org/springframework/jdbc/datasource/LazyConnectionDataSourceProxyTests.java b/spring-jdbc/src/test/java/org/springframework/jdbc/datasource/LazyConnectionDataSourceProxyTests.java
index 7159752118bf..289b1b8e6e73 100644
--- a/spring-jdbc/src/test/java/org/springframework/jdbc/datasource/LazyConnectionDataSourceProxyTests.java
+++ b/spring-jdbc/src/test/java/org/springframework/jdbc/datasource/LazyConnectionDataSourceProxyTests.java
@@ -29,6 +29,9 @@
 
 import static java.sql.Connection.TRANSACTION_NONE;
 import static java.sql.Connection.TRANSACTION_READ_COMMITTED;
+import static java.sql.Connection.TRANSACTION_READ_UNCOMMITTED;
+import static java.sql.Connection.TRANSACTION_REPEATABLE_READ;
+import static java.sql.Connection.TRANSACTION_SERIALIZABLE;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
 
@@ -75,16 +78,20 @@ void setDefaultTransactionIsolationNameToAllSupportedValues() {
 
 	@Test
 	void setDefaultTransactionIsolation() {
-		// unsupported values are not checked:
-		proxy.setDefaultTransactionIsolation(-999);
-		assertThat(proxy.defaultTransactionIsolation()).isEqualTo(-999);
-
-		// TRANSACTION_NONE should not be supported, but we currently do not check that.
-		proxy.setDefaultTransactionIsolation(TRANSACTION_NONE);
-		assertThat(proxy.defaultTransactionIsolation()).isEqualTo(TRANSACTION_NONE);
+		assertThatIllegalArgumentException().isThrownBy(() -> proxy.setDefaultTransactionIsolation(-999));
+		assertThatIllegalArgumentException().isThrownBy(() -> proxy.setDefaultTransactionIsolation(TRANSACTION_NONE));
 
 		proxy.setDefaultTransactionIsolation(TRANSACTION_READ_COMMITTED);
 		assertThat(proxy.defaultTransactionIsolation()).isEqualTo(TRANSACTION_READ_COMMITTED);
+
+		proxy.setDefaultTransactionIsolation(TRANSACTION_READ_UNCOMMITTED);
+		assertThat(proxy.defaultTransactionIsolation()).isEqualTo(TRANSACTION_READ_UNCOMMITTED);
+
+		proxy.setDefaultTransactionIsolation(TRANSACTION_REPEATABLE_READ);
+		assertThat(proxy.defaultTransactionIsolation()).isEqualTo(TRANSACTION_REPEATABLE_READ);
+
+		proxy.setDefaultTransactionIsolation(TRANSACTION_SERIALIZABLE);
+		assertThat(proxy.defaultTransactionIsolation()).isEqualTo(TRANSACTION_SERIALIZABLE);
 	}