diff --git a/renderdoc/driver/gl/gl_overlay.cpp b/renderdoc/driver/gl/gl_overlay.cpp
index 76cb3f9c4..0f272826e 100644
--- a/renderdoc/driver/gl/gl_overlay.cpp
+++ b/renderdoc/driver/gl/gl_overlay.cpp
@@ -419,6 +419,26 @@ ResourceId GLReplay::RenderOverlay(ResourceId texid, const Subresource &sub, Com
       drv.glTexParameteri(texBindingEnum, eGL_TEXTURE_WRAP_S, eGL_CLAMP_TO_EDGE);
       drv.glTexParameteri(texBindingEnum, eGL_TEXTURE_WRAP_T, eGL_CLAMP_TO_EDGE);
     }
+
+    // clear all mips first
+    drv.glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
+    drv.glDisable(eGL_BLEND);
+    drv.glDisable(eGL_SCISSOR_TEST);
+    drv.glDepthMask(GL_FALSE);
+    drv.glDisable(eGL_CULL_FACE);
+    drv.glDisable(eGL_DEPTH_TEST);
+    drv.glDisable(eGL_STENCIL_TEST);
+    drv.glStencilMask(0);
+
+    GLfloat black[4] = {};
+    for(GLint i = 0; i < texMips; i++)
+    {
+      drv.glFramebufferTexture2D(eGL_FRAMEBUFFER, eGL_COLOR_ATTACHMENT0, texBindingEnum,
+                                 DebugData.overlayTex, i);
+      drv.glClearBufferfv(eGL_COLOR, 0, black);
+    }
+
+    // bind the desired mip
     drv.glFramebufferTexture2D(eGL_FRAMEBUFFER, eGL_COLOR_ATTACHMENT0, texBindingEnum,
                                DebugData.overlayTex, sub.mip);
 
diff --git a/util/test/demos/gl/gl_overlay_test.cpp b/util/test/demos/gl/gl_overlay_test.cpp
index 9c8212a54..f904e939e 100644
--- a/util/test/demos/gl/gl_overlay_test.cpp
+++ b/util/test/demos/gl/gl_overlay_test.cpp
@@ -192,6 +192,18 @@ void main()
 
     GLuint subfbo = MakeFBO();
     glBindFramebuffer(GL_FRAMEBUFFER, subfbo);
+
+    // clear all mips/slices first
+    GLfloat black[4] = {};
+    for(GLint s = 0; s < 5; s++)
+    {
+      for(GLint m = 0; m < 4; m++)
+      {
+        glFramebufferTextureLayer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, subtex, m, s);
+        glClearBufferfv(GL_COLOR, 0, black);
+      }
+    }
+
     glFramebufferTextureLayer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, subtex, 2, 2);
 
     while(Running())