diff --git a/src/test/java/org/eolang/jeo/representation/directives/OpcodeNameTest.java b/src/test/java/org/eolang/jeo/representation/directives/OpcodeNameTest.java
index f103ca09c..100291990 100644
--- a/src/test/java/org/eolang/jeo/representation/directives/OpcodeNameTest.java
+++ b/src/test/java/org/eolang/jeo/representation/directives/OpcodeNameTest.java
@@ -61,7 +61,7 @@ void returnsOpcode() {
             .code();
         MatcherAssert.assertThat(
             String.format(
-                "Opcode code: %s does not matches with expected: %s",
+                "Opcode code: %d does not matches with expected: %d",
                 code,
                 expected
             ),