diff --git a/src/tools/KernelFunctions.cpp b/src/tools/KernelFunctions.cpp
index 2046a4374ff0c393ed78a202a5182c96ecc7b8c6..3ca72d6c74eb30516c54226390099ebc4fd2bc8d 100644
--- a/src/tools/KernelFunctions.cpp
+++ b/src/tools/KernelFunctions.cpp
@@ -100,7 +100,10 @@ width(sig)
       ktype=uniform;
   } else if(type=="TRIANGULAR" || type=="triangular"){
       ktype=triangular;
+  } else {
+      plumed_merror(type+" is an invalid kernel type\n");
   }
+  
 
   if( norm ){
     double det;