diff --git a/examples/2D_shockdroplet_muscl/case.py b/examples/2D_shockdroplet_muscl/case.py
index 61b904ec85..4367cd079a 100755
--- a/examples/2D_shockdroplet_muscl/case.py
+++ b/examples/2D_shockdroplet_muscl/case.py
@@ -64,8 +64,8 @@
             "riemann_solver": "hllc",
             "wave_speeds": "direct",
             "avg_state": "arithmetic",
-            "bc_x%beg": -6,  # 11,
-            "bc_x%end": -6,  # 12
+            "bc_x%beg": -3,
+            "bc_x%end": -3,
             "bc_y%beg": -2,
             "bc_y%end": -3,
             # Formatted Database Files Structure Parameters
diff --git a/examples/3D_shockdroplet_muscl/case.py b/examples/3D_shockdroplet_muscl/case.py
index 8213b85105..67bd4954e5 100644
--- a/examples/3D_shockdroplet_muscl/case.py
+++ b/examples/3D_shockdroplet_muscl/case.py
@@ -206,8 +206,8 @@
             "riemann_solver": "hllc",
             "wave_speeds": "direct",
             "avg_state": "arithmetic",
-            "bc_x%beg": -6,
-            "bc_x%end": -6,
+            "bc_x%beg": -3,
+            "bc_x%end": -3,
             "bc_y%beg": -2,
             "bc_y%end": -3,
             "bc_z%beg": -2,
diff --git a/toolchain/mfc/case_validator.py b/toolchain/mfc/case_validator.py
index 2167c3f749..600b0ba9f0 100644
--- a/toolchain/mfc/case_validator.py
+++ b/toolchain/mfc/case_validator.py
@@ -374,6 +374,11 @@ def _check_order_fits_grid(self, order: int, param_name: str) -> None:
     def _get_recon_type(self) -> int:
         return self.get("recon_type", 1)
 
+    def _characteristic_bcs(self) -> list:
+        """Names of the boundaries set to a characteristic BC, BC_CHAR_SLIP_WALL (-5) to BC_CHAR_SUP_OUTFLOW (-12)"""
+        names = [f"bc_{d}%{b}" for d in ["x", "y", "z"] for b in ["beg", "end"]]
+        return [name for name in names if self.get(name) is not None and -12 <= self.get(name) <= -5]
+
     def check_parameter_types(self):
         """Validate parameter types before other checks.
 
@@ -1398,6 +1403,10 @@ def check_muscl_simulation(self):
         muscl_lim = self.get("muscl_lim")
         muscl_eps = self.get("muscl_eps")
 
+        # s_cbc computes characteristic fluxes for WENO only, so MUSCL would silently ignore a CBC
+        for name in self._characteristic_bcs():
+            self.prohibit(True, f"Characteristic boundary condition {name} is not compatible with recon_type = 2 (MUSCL)")
+
         if muscl_order is None:
             return
 
@@ -1689,13 +1698,8 @@ def check_igr_simulation(self):
         self.prohibit(probe_wrt, "IGR does not support probe writes")
         self.prohibit(int_comp > 0, "IGR does not support int_comp > 0")
 
-        # Check BCs - IGR does not support characteristic BCs
-        # Characteristic BCs are BC_CHAR_SLIP_WALL (-5) through BC_CHAR_SUP_OUTFLOW (-12)
-        for dir in ["x", "y", "z"]:
-            for bound in ["beg", "end"]:
-                bc = self.get(f"bc_{dir}%{bound}")
-                if bc is not None:
-                    self.prohibit(-12 <= bc <= -5, f"Characteristic boundary condition bc_{dir}%{bound} is not compatible with IGR")
+        for name in self._characteristic_bcs():
+            self.prohibit(True, f"Characteristic boundary condition {name} is not compatible with IGR")
 
     def check_acoustic_source(self):
         """Checks acoustic source parameters (simulation)"""
diff --git a/toolchain/mfc/test_case_validator.py b/toolchain/mfc/test_case_validator.py
index 3f4a8aa728..3b3281a571 100644
--- a/toolchain/mfc/test_case_validator.py
+++ b/toolchain/mfc/test_case_validator.py
@@ -714,3 +714,18 @@ def test_rejects_isothermal_wall_without_any_heat_path(self):
             {**BASE, "bc_x%beg": -16, "bc_x%end": -16, "bc_x%isothermal_in": "T", "bc_x%Twall_in": 300.0},
             "requires a heat-conduction path",
         )
+
+
+class TestMusclCharacteristicBcs(ConstraintTestCase):
+    """s_cbc computes characteristic fluxes for WENO only, so MUSCL silently ignored a CBC."""
+
+    MUSCL = {**{k: v for k, v in BASE.items() if not k.startswith("weno")}, "recon_type": 2, "muscl_order": 2, "muscl_lim": 1}
+
+    def test_rejects_cbc_with_muscl(self):
+        self.assertRejects({**self.MUSCL, "bc_x%end": -6}, "bc_x%end is not compatible with recon_type = 2 (MUSCL)")
+
+    def test_accepts_non_characteristic_bc_with_muscl(self):
+        self.assertAccepts({**self.MUSCL, "bc_x%beg": -3, "bc_x%end": -3})
+
+    def test_accepts_cbc_with_weno(self):
+        self.assertAccepts({**BASE, "bc_x%beg": -6, "bc_x%end": -6})