diff --git a/interfaces/matlab/toolbox/1D/@Domain1D/isFlow.m b/interfaces/matlab/toolbox/1D/@Domain1D/isFlow.m
index e359f1312..f999841a0 100644
--- a/interfaces/matlab/toolbox/1D/@Domain1D/isFlow.m
+++ b/interfaces/matlab/toolbox/1D/@Domain1D/isFlow.m
@@ -8,7 +8,9 @@ function a = isFlow(d)
 %
 
 t = domainType(d);
-if t == 50
+
+% See Domain1D.h for definitions of constants
+if t < 100
     a = 1;
 else
     a = 0;