diff --git a/state_machine_exporter/src/main/java/click/kamil/springstatemachineexporter/ast/common/CodebaseContext.java b/state_machine_exporter/src/main/java/click/kamil/springstatemachineexporter/ast/common/CodebaseContext.java
index 922091c..6271b04 100644
--- a/state_machine_exporter/src/main/java/click/kamil/springstatemachineexporter/ast/common/CodebaseContext.java
+++ b/state_machine_exporter/src/main/java/click/kamil/springstatemachineexporter/ast/common/CodebaseContext.java
@@ -442,6 +442,12 @@ public class CodebaseContext {
         }
         if (!visited.add(cleanName)) return;
 
+        // Fail closed on ambiguous simple type names: we must not pick an arbitrary FQN and widen
+        // to unrelated implementations across packages.
+        if (cleanName != null && !cleanName.contains(".") && ambiguousSimpleNames.contains(cleanName)) {
+            return;
+        }
+
         // Try direct match
         List<String> directImpls = interfaceToImpls.get(cleanName);
         
diff --git a/state_machine_exporter/src/test/java/click/kamil/springstatemachineexporter/ast/common/CodebaseContextTest.java b/state_machine_exporter/src/test/java/click/kamil/springstatemachineexporter/ast/common/CodebaseContextTest.java
index 690faed..322f432 100644
--- a/state_machine_exporter/src/test/java/click/kamil/springstatemachineexporter/ast/common/CodebaseContextTest.java
+++ b/state_machine_exporter/src/test/java/click/kamil/springstatemachineexporter/ast/common/CodebaseContextTest.java
@@ -250,6 +250,29 @@ class CodebaseContextTest {
         assertThat(context.getEnumValues("b.OrderEvent")).containsExactly("b.OrderEvent.SHIP");
     }
 
+    @Test
+    void getImplementationsShouldFailClosedForAmbiguousSimpleTypeName() throws IOException {
+        Files.createDirectories(tempDir.resolve("a"));
+        Files.createDirectories(tempDir.resolve("b"));
+        Files.writeString(tempDir.resolve("a/Service.java"),
+                "package a; public interface Service {}");
+        Files.writeString(tempDir.resolve("a/AServiceImpl.java"),
+                "package a; public class AServiceImpl implements Service {}");
+        Files.writeString(tempDir.resolve("b/Service.java"),
+                "package b; public interface Service {}");
+        Files.writeString(tempDir.resolve("b/BServiceImpl.java"),
+                "package b; public class BServiceImpl implements Service {}");
+
+        CodebaseContext context = new CodebaseContext();
+        context.scan(tempDir);
+
+        assertThat(context.getImplementations("Service"))
+                .as("ambiguous simple interface name must not widen to arbitrary impls")
+                .isEmpty();
+        assertThat(context.getImplementations("a.Service")).contains("a.AServiceImpl");
+        assertThat(context.getImplementations("b.Service")).contains("b.BServiceImpl");
+    }
+
     @Test
     void shouldFindClassWithFullyQualifiedAnnotation() throws IOException {
         String source = """