diff --git a/src/main/java/org/apache/maven/plugin/compiler/AbstractCompilerMojo.java b/src/main/java/org/apache/maven/plugin/compiler/AbstractCompilerMojo.java
index 2dc4ddb8..2229dd8b 100644
--- a/src/main/java/org/apache/maven/plugin/compiler/AbstractCompilerMojo.java
+++ b/src/main/java/org/apache/maven/plugin/compiler/AbstractCompilerMojo.java
@@ -1239,7 +1239,9 @@ public void execute() throws MojoExecutionException, CompilationFailureException
             }
         }
 
-        if (outputTimestamp != null && (outputTimestamp.length() > 1 || Character.isDigit(outputTimestamp.charAt(0)))) {
+        if (outputTimestamp != null
+                && !outputTimestamp.isEmpty()
+                && (outputTimestamp.length() > 1 || Character.isDigit(outputTimestamp.charAt(0)))) {
             // if Reproducible Builds mode, apply workaround
             patchJdkModuleVersion(compilerResult, sources);
         }