diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index fc73b2c..12c21d7 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -822,7 +822,7 @@
             break;
 #endif
         default:
-            return( PSA_ERROR_NOT_SUPPORTED );
+            return( PSA_ERROR_BAD_STATE );
     }
     operation->alg = 0;
     return( PSA_SUCCESS );
@@ -1231,7 +1231,11 @@
             }
             else
 #endif /* MBEDTLS_MD_C */
-                return( PSA_ERROR_NOT_SUPPORTED );
+            {
+                /* Sanity check (shouldn't happen: operation->alg should
+                 * always have been initialized to a valid value). */
+                return( PSA_ERROR_BAD_STATE );
+            }
     }
 
     operation->alg = 0;
@@ -2218,6 +2222,11 @@
     if( operation->alg == 0 )
         return( PSA_SUCCESS );
 
+    /* Sanity check (shouldn't happen: operation->alg should
+     * always have been initialized to a valid value). */
+    if( ! PSA_ALG_IS_CIPHER( operation->alg ) )
+        return( PSA_ERROR_BAD_STATE );
+
     mbedtls_cipher_free( &operation->ctx.cipher );
 
     operation->alg = 0;