diff --git a/src/gui/render/renderGL.cpp b/src/gui/render/renderGL.cpp
index 742f668d0..2d6c338c3 100644
--- a/src/gui/render/renderGL.cpp
+++ b/src/gui/render/renderGL.cpp
@@ -107,12 +107,13 @@ const char* sh_oscRender_srcF=
   "  vec2 tresh = vec2(1.0,1.0)/uResolution;\n"
   "  float x = uv.x-uAdvance*uLineWidth*0.5;\n"
   "  float xMax = uv.x+uAdvance*uLineWidth*0.5;\n"
+  "  float alpha = 0.0;\n"
   "  float alphaX = 0.0;\n"
   "  float valmax = -1024.0;\n"
   "  float valmin = 1024.0;\n"
   "  for (; x<xMax; x+=uAdvance) {\n"
   "    float val=texture2D(oscVal,vec2(x,1.0)).x;\n"
-  "    alphaX+=0;\n"
+  "    alphaX+=0.0;\n"
   "    if (val>valmax) valmax=val;\n"
   "    if (val<valmin) valmin=val;\n"
   "  }\n"