diff --git a/libraries/pbrlib/genglsl/mx_roughness_dual.glsl b/libraries/pbrlib/genglsl/mx_roughness_dual.glsl
index a3d1f4413e..f4b538399e 100644
--- a/libraries/pbrlib/genglsl/mx_roughness_dual.glsl
+++ b/libraries/pbrlib/genglsl/mx_roughness_dual.glsl
@@ -1,5 +1,9 @@
 void mx_roughness_dual(vec2 roughness, out vec2 result)
 {
+    if (roughness.y < 0.0)
+    {
+        roughness.y = roughness.x;
+    }
     result.x = clamp(roughness.x * roughness.x, M_FLOAT_EPS, 1.0);
     result.y = clamp(roughness.y * roughness.y, M_FLOAT_EPS, 1.0);
 }
diff --git a/libraries/pbrlib/genosl/mx_roughness_dual.osl b/libraries/pbrlib/genosl/mx_roughness_dual.osl
index 42d04cd909..ea683def05 100644
--- a/libraries/pbrlib/genosl/mx_roughness_dual.osl
+++ b/libraries/pbrlib/genosl/mx_roughness_dual.osl
@@ -1,5 +1,9 @@
 void mx_roughness_dual(vector2 roughness, output vector2 result)
 {
+    if (roughness.y < 0.0)
+    {
+        roughness.y = roughness.x;
+    }
     result.x = clamp(roughness.x * roughness.x, M_FLOAT_EPS, 1.0);
     result.y = clamp(roughness.y * roughness.y, M_FLOAT_EPS, 1.0);
 }