diff --git a/deepxde/backend/paddle/tensor.py b/deepxde/backend/paddle/tensor.py
index 1f59fb5e4..713ac9f58 100644
--- a/deepxde/backend/paddle/tensor.py
+++ b/deepxde/backend/paddle/tensor.py
@@ -231,9 +231,9 @@ def sparse_dense_matmul(x, y):
     return paddle.sparse.matmul(x, y)
 
 
-def l1_regularization(x):
-    return paddle.regularizer.L1Decay(coeff=x)
+def l1_regularization(l1):
+    return paddle.regularizer.L1Decay(coeff=l1)
 
 
-def l2_regularization(x):
-    return paddle.regularizer.L2Decay(coeff=x)
+def l2_regularization(l2):
+    return paddle.regularizer.L2Decay(coeff=l2)
diff --git a/deepxde/backend/tensorflow_compat_v1/tensor.py b/deepxde/backend/tensorflow_compat_v1/tensor.py
index cc928bdc5..52270260b 100644
--- a/deepxde/backend/tensorflow_compat_v1/tensor.py
+++ b/deepxde/backend/tensorflow_compat_v1/tensor.py
@@ -247,13 +247,13 @@ def sparse_dense_matmul(x, y):
     return tf.sparse.sparse_dense_matmul(x, y)
 
 
-def l1_regularization(x):
-    return tf.keras.regularizers.L1(l1=x)
+def l1_regularization(l1):
+    return tf.keras.regularizers.L1(l1=l1)
 
 
-def l2_regularization(x):
-    return tf.keras.regularizers.L2(l2=x)
+def l2_regularization(l2):
+    return tf.keras.regularizers.L2(l2=l2)
 
 
-def l1_l2_regularization(x, y):
-    return tf.keras.regularizers.L1L2(l1=x, l2=y)
+def l1_l2_regularization(l1, l2):
+    return tf.keras.regularizers.L1L2(l1=l1, l2=l2)
diff --git a/deepxde/nn/regularizers.py b/deepxde/nn/regularizers.py
index 5cc8686e1..0e63d2bfc 100644
--- a/deepxde/nn/regularizers.py
+++ b/deepxde/nn/regularizers.py
@@ -29,5 +29,6 @@ def get(identifier):
     if name in ("l1l2", "l1+l2"):
         # TODO: only supported by 'tensorflow.compat.v1' now.
         if len(factor) < 2:
-            return bkd.l1_l2_regularization(factor[0], factor[1])
+            raise ValueError("L1L2 regularizer requires both L1/L2 penalties.")
+        return bkd.l1_l2_regularization(factor[0], factor[1])
     raise ValueError(f"Unknown regularizer name: {name}")