diff --git a/spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/support/SpringMvcContract.java b/spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/support/SpringMvcContract.java
index 5bf64653..9d9d7a8c 100644
--- a/spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/support/SpringMvcContract.java
+++ b/spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/support/SpringMvcContract.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2013-2025 the original author or authors.
+ * Copyright 2013-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -369,10 +369,7 @@ public class SpringMvcContract extends Contract.BaseContract implements Resource
 				data.template().query(resolve(nameValueResolver.getName()), resolve(nameValueResolver.getValue()));
 			}
 			else {
-				if (LOG.isDebugEnabled()) {
-					LOG.debug("Negated params are not supported by Feign and ignored during parameter processing: "
-							+ param);
-				}
+				throw new IllegalArgumentException("Negated params are not supported: " + param);
 			}
 		}
 	}
diff --git a/spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/support/SpringMvcContractTests.java b/spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/support/SpringMvcContractTests.java
index 0266a5ec..02219e2c 100644
--- a/spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/support/SpringMvcContractTests.java
+++ b/spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/support/SpringMvcContractTests.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2013-2025 the original author or authors.
+ * Copyright 2013-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -68,7 +68,6 @@ import static com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility.NONE;
 import static feign.CollectionFormat.CSV;
 import static feign.CollectionFormat.SSV;
 import static org.assertj.core.api.Assertions.assertThat;
-import static org.assertj.core.api.Assertions.assertThatCode;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
 import static org.junit.jupiter.api.Assumptions.assumeTrue;
@@ -510,11 +509,11 @@ class SpringMvcContractTests {
 	}
 
 	@Test
-	void testProcessAnnotations_ParseParams_NegatedParams() {
-		assertThatCode(() -> {
-			Method method = TestTemplate_ParseParams.class.getDeclaredMethod("negatedParams");
+	void testProcessAnnotations_ParseParams_NotEqualParams() throws Exception {
+		assertThatIllegalArgumentException().isThrownBy(() -> {
+			Method method = TestTemplate_ParseParams.class.getDeclaredMethod("notEqualParams");
 			contract.parseAndValidateMetadata(method.getDeclaringClass(), method);
-		}).doesNotThrowAnyException();
+		});
 	}
 
 	@Test
@@ -832,7 +831,7 @@ class SpringMvcContractTests {
 		ResponseEntity<TestObject> mixParams();
 
 		@GetMapping(value = "test", params = { "p1!=1" })
-		ResponseEntity<TestObject> negatedParams();
+		ResponseEntity<TestObject> notEqualParams();
 
 		@GetMapping(value = "test", params = { "p1=1" })
 		ResponseEntity<TestObject> paramsAndRequestParam(@RequestParam("p2") String p2);