diff --git a/plugins/custom-definesandincludes/compilerprovider/compilerprovider.cpp b/plugins/custom-definesandincludes/compilerprovider/compilerprovider.cpp
--- a/plugins/custom-definesandincludes/compilerprovider/compilerprovider.cpp
+++ b/plugins/custom-definesandincludes/compilerprovider/compilerprovider.cpp
@@ -138,6 +138,10 @@
     if (item) {
         languageType = Utils::languageType(item->path(), config.parserArguments.parseAmbiguousAsCPP);
     }
+    // If called on files that we can't compile, return an empty set of defines.
+    if (languageType == Utils::Other) {
+        return {};
+    }
 
     return config.compiler->defines(languageType,
         languageType == Utils::C ? config.parserArguments.cArguments : config.parserArguments.cppArguments);
@@ -150,6 +154,10 @@
     if (item) {
         languageType = Utils::languageType(item->path(), config.parserArguments.parseAmbiguousAsCPP);
     }
+    // If called on files that we can't compile, return an empty set of includes.
+    if (languageType == Utils::Other) {
+        return {};
+    }
 
     return config.compiler->includes(languageType,
         languageType == Utils::C ? config.parserArguments.cArguments : config.parserArguments.cppArguments);