diff --git a/src/dmd/typesem.d b/src/dmd/typesem.d
index 17a5603cd8fa..6221f1173885 100644
--- a/src/dmd/typesem.d
+++ b/src/dmd/typesem.d
@@ -1928,6 +1928,12 @@ Type merge(Type type)
         case Tinstance:
             return type;
 
+        case Tsarray:
+            // prevents generating the mangle if the array dim is not yet known
+            if (!(cast(TypeSArray) type).dim.isIntegerExp())
+                return type;
+            goto default;
+
         case Tenum:
             break;
 
diff --git a/test/compilable/b20045.d b/test/compilable/b20045.d
new file mode 100644
index 000000000000..988bbca5d96f
--- /dev/null
+++ b/test/compilable/b20045.d
@@ -0,0 +1,2 @@
+alias U = const ubyte[uint.sizeof]*;
+static assert (is(U == const(ubyte[4]*)));