diff --git a/org/qmckl_sherman_morrison_woodbury.org b/org/qmckl_sherman_morrison_woodbury.org
index 4ea6059..55d639d 100644
--- a/org/qmckl_sherman_morrison_woodbury.org
+++ b/org/qmckl_sherman_morrison_woodbury.org
@@ -129,6 +129,13 @@ static inline qmckl_exit_code qmckl_sherman_morrison_{Dim}(const qmckl_context c
                                 double* Slater_inv,
                                 double* determinant) {
 
+  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
+    return qmckl_failwith( context,
+                           QMCKL_NULL_CONTEXT,
+                           "qmckl_sherman_morrison_{Dim}",
+                           NULL);
+  }
+
 // TODO: Specialize for padding
 //  const uint LDS=(1+({Dim}-1)/SIMD) * SIMD;
   const uint LDS={Dim};
@@ -231,7 +238,10 @@ qmckl_exit_code qmckl_sherman_morrison(const qmckl_context context,
                                 double* determinant) {
 
   if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
-    return QMCKL_NULL_CONTEXT;
+    return qmckl_failwith( context,
+                           QMCKL_NULL_CONTEXT,
+                           "qmckl_sherman_morrison",
+                           NULL);
   }
 
   if (Dim == LDS) {