diff --git a/symbols/bound.py b/symbols/bound.py
index 7cf55ddc3..7f6d32806 100644
--- a/symbols/bound.py
+++ b/symbols/bound.py
@@ -50,8 +50,15 @@ def make_node(lower, upper, lineno):
 
         if isinstance(lower, SymbolVAR):
             lower = lower.value
+            if lower is None:  # semantic error
+                syntax_error(lineno, "Unknown lower bound for array dimension")
+                return
+
         if isinstance(upper, SymbolVAR):
             upper = upper.value
+            if upper is None:  # semantic error
+                syntax_error(lineno, "Unknown upper bound for array dimension")
+                return
 
         lower.value = int(lower.value)
         upper.value = int(upper.value)
diff --git a/tests/functional/dim_const_crash.bas b/tests/functional/dim_const_crash.bas
new file mode 100644
index 000000000..e0f27a17d
--- /dev/null
+++ b/tests/functional/dim_const_crash.bas
@@ -0,0 +1,4 @@
+
+const MAXMOBS as ubyte = MHEIGHT
+dim mobCoords(0 to MAXMOBS, 0 to 1) as ubyte
+