diff --git a/jsoncdb/org.eclipse.cdt.jsoncdb.core/src/org/eclipse/cdt/jsoncdb/core/CompileCommandsJsonParser.java b/jsoncdb/org.eclipse.cdt.jsoncdb.core/src/org/eclipse/cdt/jsoncdb/core/CompileCommandsJsonParser.java
index 9be7d1f79d4..898dd62b6d5 100644
--- a/jsoncdb/org.eclipse.cdt.jsoncdb.core/src/org/eclipse/cdt/jsoncdb/core/CompileCommandsJsonParser.java
+++ b/jsoncdb/org.eclipse.cdt.jsoncdb.core/src/org/eclipse/cdt/jsoncdb/core/CompileCommandsJsonParser.java
@@ -346,7 +346,7 @@ public class CompileCommandsJsonParser {
 		Map<String, String> effectiveDefines = Stream
 				.concat(builtinDefines.entrySet().stream(), fileResult.getDefines().entrySet().stream())
 				.collect(Collectors.toMap(stringPooler.compose(Map.Entry::getKey),
-						stringPooler.compose(Map.Entry::getValue)));
+						stringPooler.compose(Map.Entry::getValue), (e1, e2) -> e1));
 		List<String> includePaths = Stream
 				.concat(fileResult.getIncludePaths().stream(), builtinDetectorsResult.getIncludePaths().stream())
 				.map(stringPooler).collect(Collectors.toList());