diff --git a/src/Magnum/Shaders/Test/FlatGLTest.cpp b/src/Magnum/Shaders/Test/FlatGLTest.cpp
index 67913e4f1..3a1b2f231 100644
--- a/src/Magnum/Shaders/Test/FlatGLTest.cpp
+++ b/src/Magnum/Shaders/Test/FlatGLTest.cpp
@@ -659,7 +659,7 @@ template<class T> void FlatGLTest::renderVertexColor2D() {
     const Float maxThreshold = 1.334f, meanThreshold = 0.015f;
     #else
     /* WebGL 1 doesn't have 8bit renderbuffer storage, so it's worse */
-    const Float maxThreshold = 1.334f, meanThreshold = 0.013f;
+    const Float maxThreshold = 15.334f, meanThreshold = 4.355f;
     #endif
     CORRADE_COMPARE_WITH(
         /* Dropping the alpha channel, as it's always 1.0 */
@@ -717,7 +717,7 @@ template<class T> void FlatGLTest::renderVertexColor3D() {
     const Float maxThreshold = 76.67f, meanThreshold = 0.072f;
     #else
     /* WebGL 1 doesn't have 8bit renderbuffer storage, so it's worse */
-    const Float maxThreshold = 76.67f, meanThreshold = 0.072f;
+    const Float maxThreshold = 76.67f, meanThreshold = 3.908f;
     #endif
     CORRADE_COMPARE_WITH(
         /* Dropping the alpha channel, as it's always 1.0 */
diff --git a/src/Magnum/Shaders/Test/PhongGLTest.cpp b/src/Magnum/Shaders/Test/PhongGLTest.cpp
index 4d735050c..b4e2f2772 100644
--- a/src/Magnum/Shaders/Test/PhongGLTest.cpp
+++ b/src/Magnum/Shaders/Test/PhongGLTest.cpp
@@ -882,7 +882,7 @@ template<class T> void PhongGLTest::renderVertexColor() {
     const Float maxThreshold = 105.4f, meanThreshold = 0.075f;
     #else
     /* WebGL 1 doesn't have 8bit renderbuffer storage, so it's worse */
-    const Float maxThreshold = 105.4f, meanThreshold = 0.075f;
+    const Float maxThreshold = 105.4f, meanThreshold = 3.254f;
     #endif
     CORRADE_COMPARE_WITH(
         /* Dropping the alpha channel, as it's always 1.0 */