diff --git a/mplot/VisualDefaultShaders.h b/mplot/VisualDefaultShaders.h
index 5d2fff3d..71ed7acf 100644
--- a/mplot/VisualDefaultShaders.h
+++ b/mplot/VisualDefaultShaders.h
@@ -16,9 +16,9 @@ namespace mplot
     "uniform float alpha;\n";
     const char* defaultVtxShader_instance_uniforms =
     "uniform mat4 s_matrix;\n" // scaling matrix
-    "uniform int instance_count = 0;\n"
-    "uniform int instance_start = -1;\n"
-    "uniform int instparam_count = 0;\n";
+    "uniform int instance_count;\n"
+    "uniform int instance_start;\n"
+    "uniform int instparam_count;\n";
     const char* defaultVtxShader_part1b =
     "layout(location = 0) in vec4 position;\n"
     "layout(location = 1) in vec4 normalin;\n"
@@ -50,7 +50,11 @@ namespace mplot
     "{\n"
     "    if (instance_count > 0) {\n"
     "        int ipos_i = instance_start * 3 + gl_InstanceID * 3;\n"
-    "        vec4 iposv = { ipos[ipos_i], ipos[ipos_i + 1], ipos[ipos_i + 2], 0 };\n"
+    "        vec4 iposv;\n"
+    "        iposv[0] = ipos[ipos_i];\n"
+    "        iposv[1] = ipos[ipos_i + 1];\n"
+    "        iposv[2] = ipos[ipos_i + 2];\n"
+    "        iposv[3] = 0.0;\n"
     "        if (instparam_count > 0) {\n"
     "            int idx = gl_InstanceID % instparam_count;\n"
     "            int ippos_i = instance_start * 5;\n"
diff --git a/shaders/Visual_instancing.vert.glsl b/shaders/Visual_instancing.vert.glsl
index e11e5e8d..6aed531a 100644
--- a/shaders/Visual_instancing.vert.glsl
+++ b/shaders/Visual_instancing.vert.glsl
@@ -3,9 +3,9 @@ uniform mat4 m_matrix;
 uniform mat4 v_matrix;
 uniform mat4 p_matrix;
 uniform float alpha;
-uniform int instance_count = 0;
-uniform int instance_start = -1;
-uniform int instparam_count = 0;
+uniform int instance_count;
+uniform int instance_start;
+uniform int instparam_count;
 layout(location = 0) in vec4 position;
 layout(location = 1) in vec4 normalin;
 layout(location = 2) in vec3 color;
@@ -21,7 +21,11 @@ void main()
 {
     if (instance_count > 0) {
         int ipos_i = instance_start * 3 + gl_InstanceID * 3;
-        vec4 iposv = { ipos[ipos_i], ipos[ipos_i + 1], ipos[ipos_i + 2], 0 };
+        vec4 iposv;
+        iposv[0] = ipos[ipos_i];
+        iposv[1] = ipos[ipos_i + 1];
+        iposv[2] = ipos[ipos_i + 2];
+        iposv[3] = 0.0;
         if (instparam_count > 0) {
             int idx = gl_InstanceID % instparam_count;
             int ippos_i = instance_start * 5;