diff --git a/renderdocui/Code/FormatElement.cs b/renderdocui/Code/FormatElement.cs
index e7edc5bee..754b01e5a 100644
--- a/renderdocui/Code/FormatElement.cs
+++ b/renderdocui/Code/FormatElement.cs
@@ -500,6 +500,10 @@ namespace renderdocui.Code
                 uint matrixCount = 0;
                 uint width = 0;
 
+                // check for square matrix declarations like 'mat4' and 'mat3'
+                if (basetype == "mat" && !match.Groups[4].Success)
+                    matrixDim = vectorDim;
+
                 // calculate format
                 {
                     if (!uint.TryParse(vectorDim, out count))