diff --git a/src/MAT_v5.jl b/src/MAT_v5.jl
index 1b81261..aa9e2b6 100644
--- a/src/MAT_v5.jl
+++ b/src/MAT_v5.jl
@@ -374,7 +374,7 @@ function getvarnames(matfile::Matlabv5File)
                 dest = zeros(Uint8, 1024)
                 dest_buf_size = Int[1024]
 
-                ret = ccall((:uncompress, @windows ? "zlib1" : "libz"), Int32, (Ptr{Uint}, Ptr{Uint}, Ptr{Uint}, Uint),
+                ret = ccall((:uncompress, @windows ? "zlib1" : "libz"), Int32, (Ptr{Uint8}, Ptr{Int}, Ptr{Uint8}, Uint),
                     dest, dest_buf_size, source, length(source))
 
                 # Zlib may complain because the buffer is small or the data are incomplete