diff --git a/filters/karbon/pdf/SvgOutputDev.h b/filters/karbon/pdf/SvgOutputDev.h
--- a/filters/karbon/pdf/SvgOutputDev.h
+++ b/filters/karbon/pdf/SvgOutputDev.h
@@ -62,7 +62,7 @@
     // images
     void drawImage(GfxState *state, Object *ref, Stream *str,
                            int width, int height, GfxImageColorMap *colorMap,
-                           bool interpolate, int *maskColors, bool inlineImg) override;
+                           bool interpolate, const int *maskColors, bool inlineImg) override;
 
     // styles
     void updateAll(GfxState *state) override;
diff --git a/filters/karbon/pdf/SvgOutputDev.cpp b/filters/karbon/pdf/SvgOutputDev.cpp
--- a/filters/karbon/pdf/SvgOutputDev.cpp
+++ b/filters/karbon/pdf/SvgOutputDev.cpp
@@ -417,7 +417,7 @@
 #endif
     int len = s->getLength();
     CharCode code;
-    Unicode *u = nullptr;
+    const Unicode *u = nullptr;
     int uLen;
     double dx, dy, originX, originY;
     while (len > 0) {
@@ -496,7 +496,7 @@
 
 void SvgOutputDev::drawImage(GfxState *state, Object */*ref*/, Stream *str,
                              int width, int height, GfxImageColorMap *colorMap,
-                             bool /*interpolate*/, int *maskColors, bool /*inlineImg*/)
+                             bool /*interpolate*/, const int *maskColors, bool /*inlineImg*/)
 {
     ImageStream * imgStr = new ImageStream(str, width, colorMap->getNumPixelComps(), colorMap->getBits());
     imgStr->reset();