diff --git a/src/ragas/metrics/_answer_similarity.py b/src/ragas/metrics/_answer_similarity.py
index 09b13de9b..00fd273da 100644
--- a/src/ragas/metrics/_answer_similarity.py
+++ b/src/ragas/metrics/_answer_similarity.py
@@ -70,7 +70,12 @@ def _score(self, row: t.Dict, callbacks: Callbacks) -> float:
             embeddings_1 = np.array(self.embeddings.embed_documents(ground_truths))
             embeddings_2 = np.array(self.embeddings.embed_documents(answers))
             similarity = embeddings_1 @ embeddings_2.T
-            scores = np.diagonal(similarity)
+            if similarity.size == 1:
+                # If similarity has only one value, directly use this value as scores
+                scores = similarity.flatten()
+            else:
+                # If similarity contains multiple values, extract the diagonal as scores
+                scores = np.diagonal(similarity)
 
         assert isinstance(scores, np.ndarray), "Expects ndarray"
         if self.threshold:
@@ -92,7 +97,10 @@ async def _ascore(self: t.Self, row: t.Dict, callbacks: Callbacks = []) -> float
             )
             embeddings_2 = np.array(await self.embeddings.aembed_documents(answers))
             similarity = embeddings_1 @ embeddings_2.T
-            scores = np.diagonal(similarity)
+            if similarity.size == 1:
+                scores = similarity.flatten()
+            else:
+                scores = np.diagonal(similarity)
 
         assert isinstance(scores, np.ndarray), "Expects ndarray"
         if self.threshold: