diff --git a/src/MAT_HDF5.jl b/src/MAT_HDF5.jl
index 3001e70..a4f8cbf 100644
--- a/src/MAT_HDF5.jl
+++ b/src/MAT_HDF5.jl
@@ -169,6 +169,9 @@ function m_read(dset::HDF5Dataset)
             end
         end
         return out
+    elseif !haskey(str2type_matlab,mattype)
+        @warn "MATLAB $mattype values are currently not supported"
+        return nothing
     end
 
     # Regular arrays of values