diff --git a/build.gradle b/build.gradle
index ad400436e2..3e5b94b718 100755
--- a/build.gradle
+++ b/build.gradle
@@ -34,7 +34,7 @@ ext {
     jetbrainsAnnotations: "org.jetbrains:annotations:13.0",
     ant: "org.apache.ant:ant:1.9.7",
     asm: "org.ow2.asm:asm:5.2",
-    bytebuddy: "net.bytebuddy:byte-buddy:1.7.0",
+    bytebuddy: "net.bytebuddy:byte-buddy:1.7.6",
     cglib: "cglib:cglib-nodep:3.2.5",
     groovy: "org.codehaus.groovy:groovy-all:$groovyVersion",
     h2database: "com.h2database:h2:1.3.176",
diff --git a/spock-core/src/main/java/org/spockframework/mock/runtime/ProxyBasedMockFactory.java b/spock-core/src/main/java/org/spockframework/mock/runtime/ProxyBasedMockFactory.java
index 84936e9609..0f10d9c92e 100644
--- a/spock-core/src/main/java/org/spockframework/mock/runtime/ProxyBasedMockFactory.java
+++ b/spock-core/src/main/java/org/spockframework/mock/runtime/ProxyBasedMockFactory.java
@@ -26,6 +26,7 @@
 import net.bytebuddy.*;
 import net.bytebuddy.description.modifier.*;
 import net.bytebuddy.dynamic.Transformer;
+import net.bytebuddy.dynamic.scaffold.TypeValidation;
 import net.bytebuddy.implementation.*;
 import net.bytebuddy.implementation.bind.annotation.Morph;
 import net.sf.cglib.proxy.*;
@@ -103,6 +104,7 @@ static Object createMock(final Class<?> type,
           public Class<?> call() throws Exception {
             return new ByteBuddy()
               .with(new NamingStrategy.SuffixingRandom("SpockMock"))
+              .with(TypeValidation.DISABLED) // https://github.com/spockframework/spock/issues/776
               .ignore(none())
               .subclass(type)
               .implement(additionalInterfaces)