diff --git a/rtengine/guidedfilter.cc b/rtengine/guidedfilter.cc
index 790245b20..1aad138e3 100644
--- a/rtengine/guidedfilter.cc
+++ b/rtengine/guidedfilter.cc
@@ -211,11 +211,13 @@ void guidedFilter(const array2D<float> &guide, const array2D<float> &src, array2
     f_mean(meanb, b, r1);
     DEBUG_DUMP(meanb);
 
+    blur_buf.resize(0); // frees W * H * 4 byte
+
     array2D<float> meanA(W, H);
     f_upsample(meanA, meana);
     DEBUG_DUMP(meanA);
 
-    array2D<float> meanB(W, H);
+    array2D<float> &meanB = q;
     f_upsample(meanB, meanb);
     DEBUG_DUMP(meanB);