diff --git a/rtengine/rawimagesource.cc b/rtengine/rawimagesource.cc
index 3adf92c7e..a96a834e5 100644
--- a/rtengine/rawimagesource.cc
+++ b/rtengine/rawimagesource.cc
@@ -2430,7 +2430,7 @@ void RawImageSource::bilinear_demosaic()
   {
             int tid = omp_get_thread_num();
             int nthreads = omp_get_num_threads();
-            int blk = W/nthreads;
+            int blk = H/nthreads;
 
             int start = 0;
             if (tid == 0) start = 1;