diff --git a/devtools/gradle/gradle-application-plugin/src/main/java/io/quarkus/gradle/tasks/BaseConfig.java b/devtools/gradle/gradle-application-plugin/src/main/java/io/quarkus/gradle/tasks/BaseConfig.java
index 5ea1afc05997c..e9afdb7ca7d0b 100644
--- a/devtools/gradle/gradle-application-plugin/src/main/java/io/quarkus/gradle/tasks/BaseConfig.java
+++ b/devtools/gradle/gradle-application-plugin/src/main/java/io/quarkus/gradle/tasks/BaseConfig.java
@@ -2,6 +2,7 @@
 
 import java.util.List;
 import java.util.Map;
+import java.util.TreeMap;
 import java.util.function.Predicate;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
@@ -60,6 +61,8 @@ Map<String, String> cachingRelevantProperties(List<String> propertyPatterns) {
         Predicate<Map.Entry<String, ?>> keyPredicate = e -> patterns.stream().anyMatch(p -> p.matcher(e.getKey()).matches());
         return values.entrySet().stream()
                 .filter(keyPredicate)
-                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
+                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (s, s2) -> {
+                    throw new IllegalArgumentException("Duplicate key");
+                }, TreeMap::new));
     }
 }
diff --git a/devtools/gradle/gradle-application-plugin/src/main/java/io/quarkus/gradle/tasks/QuarkusGenerateCode.java b/devtools/gradle/gradle-application-plugin/src/main/java/io/quarkus/gradle/tasks/QuarkusGenerateCode.java
index 1b1cc049c8bd5..f3b5a930bb51a 100644
--- a/devtools/gradle/gradle-application-plugin/src/main/java/io/quarkus/gradle/tasks/QuarkusGenerateCode.java
+++ b/devtools/gradle/gradle-application-plugin/src/main/java/io/quarkus/gradle/tasks/QuarkusGenerateCode.java
@@ -3,9 +3,11 @@
 import java.io.File;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.util.Collections;
 import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;
+import java.util.TreeMap;
 import java.util.stream.Collectors;
 
 import javax.inject.Inject;
@@ -76,7 +78,8 @@ Map<String, String> getInternalTaskConfig() {
         // an input to the cache key. We need to declare these properties as inputs, because those influence the
         // execution.
         // Documented here: https://docs.gradle.org/current/userguide/build_cache.html#sec:task_output_caching_inputs
-        return Map.of("launchMode", launchMode.name(), "inputSourceSetName", inputSourceSetName);
+        return Collections.unmodifiableMap(
+                new TreeMap<>(Map.of("launchMode", launchMode.name(), "inputSourceSetName", inputSourceSetName)));
     }
 
     @InputFiles