diff --git a/Source/Operator/SetBCs.cpp b/Source/Operator/SetBCs.cpp
index 9105139..f137ae6 100644
--- a/Source/Operator/SetBCs.cpp
+++ b/Source/Operator/SetBCs.cpp
@@ -43,15 +43,15 @@ void ParseBC(FArrayBox &a_state, const Box &a_valid,
 
         // this will populate the multigrid boundaries according to the BCs
         // in particular it will fill cells for Aij, and updated K
-        solver_boundaries.fill_constraint_box(Side::Lo, a_state,
-                                              Interval(0, NUM_CONSTRAINT_VARS));
-        solver_boundaries.fill_constraint_box(Side::Hi, a_state,
-                                              Interval(0, NUM_CONSTRAINT_VARS));
+        solver_boundaries.fill_constraint_box(
+            Side::Lo, a_state, Interval(0, NUM_CONSTRAINT_VARS - 1));
+        solver_boundaries.fill_constraint_box(
+            Side::Hi, a_state, Interval(0, NUM_CONSTRAINT_VARS - 1));
         // Do it twice to catch corners... must be a better way
         // but for now this works
-        solver_boundaries.fill_constraint_box(Side::Lo, a_state,
-                                              Interval(0, NUM_CONSTRAINT_VARS));
-        solver_boundaries.fill_constraint_box(Side::Hi, a_state,
-                                              Interval(0, NUM_CONSTRAINT_VARS));
+        solver_boundaries.fill_constraint_box(
+            Side::Lo, a_state, Interval(0, NUM_CONSTRAINT_VARS - 1));
+        solver_boundaries.fill_constraint_box(
+            Side::Hi, a_state, Interval(0, NUM_CONSTRAINT_VARS - 1));
     }
 }