diff --git a/build.gradle b/build.gradle
index 8bd69083a0..b6ea632902 100644
--- a/build.gradle
+++ b/build.gradle
@@ -639,7 +639,9 @@ project(':artio-session-codecs') {
     tasks.register('generateCodecs', JavaExec) {
         mainClass.set('uk.co.real_logic.artio.dictionary.CodecGenerationTool')
         classpath = configurations.codecGeneration
-        args = [generatedDir, 'src/main/resources/session_dictionary.xml']
+        def dictionaryFile = 'src/main/resources/session_dictionary.xml'
+        inputs.file(dictionaryFile)
+        args = [generatedDir, dictionaryFile]
         outputs.dir generatedDir
         systemProperty("fix.codecs.flyweight", "true")
     }
@@ -647,7 +649,9 @@ project(':artio-session-codecs') {
     tasks.register('generateOtherCodecs', JavaExec) {
         mainClass.set('uk.co.real_logic.artio.dictionary.CodecGenerationTool')
         classpath = configurations.codecGeneration
-        args = [generatedDir, 'src/main/resources/other_session_dictionary.xml']
+        def dictionaryFile = 'src/main/resources/other_session_dictionary.xml'
+        inputs.file(dictionaryFile)
+        args = [generatedDir, dictionaryFile]
         outputs.dir generatedDir
         systemProperty("fix.codecs.flyweight", "true")
         systemProperty("fix.codecs.parent_package", "uk.co.real_logic.artio.other")