diff --git a/core/src/main/java/lucee/transformer/dynamic/meta/dynamic/FunctionMemberDynamic.java b/core/src/main/java/lucee/transformer/dynamic/meta/dynamic/FunctionMemberDynamic.java
index bbc2855a0b..5f740f389e 100644
--- a/core/src/main/java/lucee/transformer/dynamic/meta/dynamic/FunctionMemberDynamic.java
+++ b/core/src/main/java/lucee/transformer/dynamic/meta/dynamic/FunctionMemberDynamic.java
@@ -369,16 +369,16 @@ public String[] getArguments() {
 	public Class[] getArgumentClasses() {
 		if (argClasses == null) {
 			ClassLoader cl = Clazz.getClassLoader(this.declaringClass);
-			argClasses = new Class[argTypes.length];
+			Class[] tmp = new Class[argTypes.length];
 			for (int i = 0; i < argTypes.length; i++) {
 				try {
-
-					argClasses[i] = Clazz.toClass(cl, argTypes[i]);
+					tmp[i] = Clazz.toClass(cl, argTypes[i]);
 				}
 				catch (ClassException e) {
 					throw new PageRuntimeException(e);
 				}
 			}
+			argClasses = tmp;
 		}
 		return argClasses;
 	}
diff --git a/loader/build.xml b/loader/build.xml
index d467b51b01..648cabeafe 100644
--- a/loader/build.xml
+++ b/loader/build.xml
@@ -2,7 +2,7 @@
 <project default="core" basedir="." name="Lucee" 
   xmlns:resolver="antlib:org.apache.maven.resolver.ant">
 
-  <property name="version" value="6.2.0.98-SNAPSHOT"/>
+  <property name="version" value="6.2.0.99-SNAPSHOT"/>
 
   <taskdef uri="antlib:org.apache.maven.resolver.ant" resource="org/apache/maven/resolver/ant/antlib.xml">
     <classpath>
diff --git a/loader/pom.xml b/loader/pom.xml
index 1b2a9fd073..1b74eb1ddb 100644
--- a/loader/pom.xml
+++ b/loader/pom.xml
@@ -3,7 +3,7 @@
 
   <groupId>org.lucee</groupId>
   <artifactId>lucee</artifactId>
-  <version>6.2.0.98-SNAPSHOT</version>
+  <version>6.2.0.99-SNAPSHOT</version>
   <packaging>jar</packaging>
 
   <name>Lucee Loader Build</name>
diff --git a/test/tickets/LDEV5103.cfc b/test/tickets/LDEV5103.cfc
new file mode 100644
index 0000000000..154384a180
--- /dev/null
+++ b/test/tickets/LDEV5103.cfc
@@ -0,0 +1,25 @@
+component extends="org.lucee.cfml.test.LuceeTestCase" skip="true" {
+
+	function run( testResults , testBox ) {
+		describe( title='LDEV-5103', body=function(){
+
+			it( title='concurrency issue in Clazz.getArgumentClasses', body=function() {
+				var names=[];
+				loop from=1 to=100 index="local.i" {
+					var name="t5103-#i#";
+					arrayAppend(names, name);
+					thread name="#name#" {
+						variables.dateParser = createObject("java", "java.text.SimpleDateFormat").init("yyyy-MM-dd'T'HH:mm:ssX");
+					}
+				}
+
+				thread action="join" name=names.toList();
+				loop array=names item="name" {
+					if(structKeyExists(cfthread[name],"ERROR")) throw cfthread[name].error;
+				}
+			});
+
+		});
+	}
+
+}
\ No newline at end of file