diff --git a/de.prob.units/src/de/prob/units/sc/ContextAttributeProcessor.java b/de.prob.units/src/de/prob/units/sc/ContextAttributeProcessor.java
index 6b420739b80577423bfb412aad576a0f86f4fae0..3b181725d3fcd1a0a21e4413489ab8fb04ef2da5 100644
--- a/de.prob.units/src/de/prob/units/sc/ContextAttributeProcessor.java
+++ b/de.prob.units/src/de/prob/units/sc/ContextAttributeProcessor.java
@@ -44,7 +44,7 @@ public class ContextAttributeProcessor extends SCProcessorModule {
 					.getIdentifierString());
 
 			// might have been filtered out by previous modules
-			if (scConstant != null) {
+			if (scConstant.exists()) {
 				// original might not contain the attribute
 				if (constant.hasAttribute(UnitPragmaAttribute.ATTRIBUTE)) {
 					String attribute = constant
diff --git a/de.prob.units/src/de/prob/units/sc/MachineAttributeProcessor.java b/de.prob.units/src/de/prob/units/sc/MachineAttributeProcessor.java
index 4c7ddd38f4a195674c5e270338b5031f1fd3f4a0..92a739fd10b4a132c66b917a0b0d74e16293b648 100644
--- a/de.prob.units/src/de/prob/units/sc/MachineAttributeProcessor.java
+++ b/de.prob.units/src/de/prob/units/sc/MachineAttributeProcessor.java
@@ -44,7 +44,7 @@ public class MachineAttributeProcessor extends SCProcessorModule {
 					.getIdentifierString());
 
 			// might have been filtered out by previous modules
-			if (scVar != null) {
+			if (scVar.exists()) {
 				// original might not contain the attribute
 				if (var.hasAttribute(UnitPragmaAttribute.ATTRIBUTE)) {
 					String attribute = var