diff --git a/unwrap2D/unwrap2D.pyx b/unwrap2D/unwrap2D.pyx
index 9bd901d5..dab52167 100755
--- a/unwrap2D/unwrap2D.pyx
+++ b/unwrap2D/unwrap2D.pyx
@@ -1,4 +1,4 @@
-cdef extern unwrap2D(float* wrapped_image, 
+cdef extern void unwrap2D(float* wrapped_image, 
                      float* unwrapped_image, 
                      unsigned char* input_mask, 
                      int image_width, int image_height,