diff --git a/include/sparta/PowersetAbstractDomain.h b/include/sparta/PowersetAbstractDomain.h
index 88e1ca5..e54131c 100644
--- a/include/sparta/PowersetAbstractDomain.h
+++ b/include/sparta/PowersetAbstractDomain.h
@@ -235,6 +235,9 @@ class PowersetAbstractDomain
       return this->get_value()->contains(e);
     }
     }
+    SPARTA_ASSERT(false && "unknown AbstractValueKind");
+    // Return false to suppress -Wreturn-type warning reported by gcc
+    return false;
   }
 
   friend std::ostream& operator<<(std::ostream& o, const Derived& s) {
diff --git a/include/sparta/SmallSortedSetAbstractDomain.h b/include/sparta/SmallSortedSetAbstractDomain.h
index 514f094..9a3229b 100644
--- a/include/sparta/SmallSortedSetAbstractDomain.h
+++ b/include/sparta/SmallSortedSetAbstractDomain.h
@@ -167,6 +167,9 @@ class SmallSortedSetAbstractDomain final
       return this->get_value()->contains(e);
     }
     }
+    SPARTA_ASSERT(false && "unknown AbstractValueKind");
+    // Return false to suppress -Wreturn-type warning reported by gcc
+    return false;
   }
 
   friend std::ostream& operator<<(std::ostream& out,