diff --git a/src/main/java/build/buf/protovalidate/internal/celext/CustomDeclarations.java b/src/main/java/build/buf/protovalidate/internal/celext/CustomDeclarations.java
index c5f6888c..f6f28114 100644
--- a/src/main/java/build/buf/protovalidate/internal/celext/CustomDeclarations.java
+++ b/src/main/java/build/buf/protovalidate/internal/celext/CustomDeclarations.java
@@ -50,9 +50,14 @@ static List<Decl> create() {
     decls.add(
         Decls.newFunction(
             "isIpPrefix",
-            Decls.newInstanceOverload("is_ip_prefix_int_bool", Arrays.asList(Decls.String, Decls.Int, Decls.Bool), Decls.Bool),
-            Decls.newInstanceOverload("is_ip_prefix_int", Arrays.asList(Decls.String, Decls.Int), Decls.Bool),
-            Decls.newInstanceOverload("is_ip_prefix_bool", Arrays.asList(Decls.String, Decls.Bool), Decls.Bool),
+            Decls.newInstanceOverload(
+                "is_ip_prefix_int_bool",
+                Arrays.asList(Decls.String, Decls.Int, Decls.Bool),
+                Decls.Bool),
+            Decls.newInstanceOverload(
+                "is_ip_prefix_int", Arrays.asList(Decls.String, Decls.Int), Decls.Bool),
+            Decls.newInstanceOverload(
+                "is_ip_prefix_bool", Arrays.asList(Decls.String, Decls.Bool), Decls.Bool),
             Decls.newInstanceOverload(
                 "is_ip_prefix", Collections.singletonList(Decls.String), Decls.Bool)));
 
diff --git a/src/main/java/build/buf/protovalidate/internal/celext/CustomOverload.java b/src/main/java/build/buf/protovalidate/internal/celext/CustomOverload.java
index f3981d4b..4d350b41 100644
--- a/src/main/java/build/buf/protovalidate/internal/celext/CustomOverload.java
+++ b/src/main/java/build/buf/protovalidate/internal/celext/CustomOverload.java
@@ -298,7 +298,8 @@ private static Overload isIpPrefix() {
         OVERLOAD_IS_IP_PREFIX,
         null,
         value -> {
-          if (value.type().typeEnum() != TypeEnum.String && value.type().typeEnum() != TypeEnum.Bool ) {
+          if (value.type().typeEnum() != TypeEnum.String
+              && value.type().typeEnum() != TypeEnum.Bool) {
             return Err.noSuchOverload(value, OVERLOAD_IS_IP_PREFIX, null);
           }
           String prefix = (String) value.value();
@@ -308,7 +309,9 @@ private static Overload isIpPrefix() {
           return Types.boolOf(validateIPPrefix(prefix, 0L, false));
         },
         (lhs, rhs) -> {
-          if (lhs.type().typeEnum() != TypeEnum.String || (rhs.type().typeEnum() != TypeEnum.Int && rhs.type().typeEnum() != TypeEnum.Bool)) {
+          if (lhs.type().typeEnum() != TypeEnum.String
+              || (rhs.type().typeEnum() != TypeEnum.Int
+                  && rhs.type().typeEnum() != TypeEnum.Bool)) {
             return Err.noSuchOverload(lhs, OVERLOAD_IS_IP_PREFIX, rhs);
           }
           String prefix = (String) lhs.value();
@@ -317,22 +320,20 @@ private static Overload isIpPrefix() {
           }
           if (rhs.type().typeEnum() == TypeEnum.Int) {
             return Types.boolOf(validateIPPrefix(prefix, rhs.intValue(), false));
-          } else if (rhs.type().typeEnum() == TypeEnum.Bool) {
-            return Types.boolOf(validateIPPrefix(prefix, 0L, rhs.booleanValue()));
           }
-          return BoolT.False;
+          return Types.boolOf(validateIPPrefix(prefix, 0L, rhs.booleanValue()));
         },
         (values) -> {
-          if (values[0].type().typeEnum() != TypeEnum.String || values[1].type().typeEnum() != TypeEnum.Int || values[2].type().typeEnum() != TypeEnum.Bool) {
-            return Err.noSuchOverload(values[0], OVERLOAD_IS_IP_PREFIX, "", new Val[]{values[1], values[2]});
+          if (values.length != 3) {
+            return Err.noSuchOverload(values[0], OVERLOAD_IS_IP_PREFIX, "", values);
           }
           String prefix = (String) values[0].value();
           if (prefix.isEmpty()) {
             return BoolT.False;
           }
-          return Types.boolOf(validateIPPrefix(prefix, values[1].intValue(), values[2].booleanValue()));
-        }
-    );
+          return Types.boolOf(
+              validateIPPrefix(prefix, values[1].intValue(), values[2].booleanValue()));
+        });
   }
 
   /**
@@ -551,7 +552,8 @@ private static boolean validateIP(String addr, long ver) {
    *
    * @param prefix The input string to validate as an IP prefix.
    * @param ver The IP version to validate against (0 for any version, 4 for IPv4, 6 for IPv6).
-   * @param strict If strict is true and host bits are set in the supplied address, then false is returned.
+   * @param strict If strict is true and host bits are set in the supplied address, then false is
+   *     returned.
    * @return {@code true} if the input string is a valid IP prefix of the specified version, {@code
    *     false} otherwise.
    */
diff --git a/src/test/java/build/buf/protovalidate/internal/celext/CustomOverloadTest.java b/src/test/java/build/buf/protovalidate/internal/celext/CustomOverloadTest.java
index 5029372a..45e901b9 100644
--- a/src/test/java/build/buf/protovalidate/internal/celext/CustomOverloadTest.java
+++ b/src/test/java/build/buf/protovalidate/internal/celext/CustomOverloadTest.java
@@ -162,6 +162,18 @@ public void testIsIpPrefix() {
     }
   }
 
+  @Test
+  public void testIsIpPrefixUnsupported() {
+    List<String> testCases = ImmutableList.of("1.isIpPrefix()");
+    for (String testCase : testCases) {
+      Program.EvalResult result = eval(testCase);
+      Val val = result.getVal();
+      assertThat(Err.isError(val)).isTrue();
+      assertThatThrownBy(() -> val.convertToNative(Exception.class))
+          .isInstanceOf(UnsupportedOperationException.class);
+    }
+  }
+
   private Program.EvalResult eval(String source) {
     return eval(source, Activation.emptyActivation());
   }