diff --git a/src/main/java/org/olat/core/util/StringHelper.java b/src/main/java/org/olat/core/util/StringHelper.java
index e7d4e98501a2c07ee7134ad3291d49add2b07135..ee27b2716833f98a379286deb98193096ad5a99c 100644
--- a/src/main/java/org/olat/core/util/StringHelper.java
+++ b/src/main/java/org/olat/core/util/StringHelper.java
@@ -404,7 +404,7 @@ public class StringHelper {
 		char[] charArr = string.toCharArray();
 		for(int i=charArr.length; i-->stop; ) {
 			char ch = charArr[i];
-			if(ch < 47 || ch > 58) {
+			if(ch < 48 || ch > 57) {
 				return false;
 			}
 		}
diff --git a/src/test/java/org/olat/core/util/StringHelperTest.java b/src/test/java/org/olat/core/util/StringHelperTest.java
index df5b39c56763f18ab80d407e9aa8417ad5df1fb9..14fa9044a1776001ff63f65c79141a62a13ba1e4 100644
--- a/src/test/java/org/olat/core/util/StringHelperTest.java
+++ b/src/test/java/org/olat/core/util/StringHelperTest.java
@@ -112,12 +112,20 @@ public class StringHelperTest {
 	@Test
 	public void isLong() {
 		Assert.assertTrue(StringHelper.isLong("234"));
+		Assert.assertTrue(StringHelper.isLong("0123456789"));
 		Assert.assertTrue(StringHelper.isLong("9223372036854775807"));
 		Assert.assertTrue(StringHelper.isLong("-9223372036854775807"));
 
+		//check some unacceptable strings
 		Assert.assertFalse(StringHelper.isLong("10223372036854775807"));
 		Assert.assertFalse(StringHelper.isLong("-dru"));
 		Assert.assertFalse(StringHelper.isLong("OpenOLAT"));
 		Assert.assertFalse(StringHelper.isLong("A very long number with a lot of characters"));
+		
+		//check ascii range
+		Assert.assertFalse(StringHelper.isLong("/"));
+		Assert.assertFalse(StringHelper.isLong(":"));
+		Assert.assertFalse(StringHelper.isLong("."));
+		Assert.assertFalse(StringHelper.isLong(";"));
 	}
 }