diff --git a/src/core/effects/qgsimageoperation.cpp b/src/core/effects/qgsimageoperation.cpp
index c5b8b6ce0ae..97789794202 100644
--- a/src/core/effects/qgsimageoperation.cpp
+++ b/src/core/effects/qgsimageoperation.cpp
@@ -771,7 +771,7 @@ inline QRgb QgsImageOperation::GaussianBlurOperation::gaussianBlurVertical( cons
   for ( int i = 0; i <= mRadius * 2; ++i )
   {
     y = std::clamp( posy + ( i - mRadius ), 0, height - 1 );
-    ref = sourceFirstLine + sourceBpl * y;
+    ref = sourceFirstLine + static_cast< std::size_t >( sourceBpl ) * y;
 
     QRgb *refRgb = reinterpret_cast< QRgb * >( ref );
     r += mKernel[i] * qRed( *refRgb );
diff --git a/src/core/effects/qgsimageoperation.h b/src/core/effects/qgsimageoperation.h
index 49de42737d0..a4d6a6ded56 100644
--- a/src/core/effects/qgsimageoperation.h
+++ b/src/core/effects/qgsimageoperation.h
@@ -445,7 +445,7 @@ class CORE_EXPORT QgsImageOperation
           int increment = ( mDirection == QgsImageOperation::ByRow ) ? 4 : bytesPerLine;
           if ( !mForwardDirection )
           {
-            p += ( lineLength - 1 ) * increment;
+            p += static_cast< std::size_t >( lineLength - 1 ) * increment;
             increment = -increment;
           }