diff --git a/creationfunctions.py b/creationfunctions.py
index 0eda27e0835a01eab46b2696cf616cc003cb6aac..5292494fe5b85d85eeb3c81e7a46e309a73b9ed0 100644
--- a/creationfunctions.py
+++ b/creationfunctions.py
@@ -185,7 +185,7 @@ def createLatticeBoltzmannAst(updateRule=None, optimizationParams={}, **kwargs):
         params['optimizationParams'] = optimizationParams
         updateRule = createLatticeBoltzmannUpdateRule(**params)
 
-    fieldTypes = set(fa.field.dtype for fa in updateRule.freeSymbols if isinstance(fa, Field.Access))
+    fieldTypes = set(fa.field.dtype for fa in updateRule.definedSymbols if isinstance(fa, Field.Access))
     res = createKernel(updateRule, target=optParams['target'], dataType=collateTypes(fieldTypes),
                        cpuOpenMP=optParams['openMP'], cpuVectorizeInfo=optParams['vectorization'],
                        gpuIndexing=optParams['gpuIndexing'], gpuIndexingParams=optParams['gpuIndexingParams'],