diff --git a/sphinxcontrib/openapi/renderers/_httpdomain.py b/sphinxcontrib/openapi/renderers/_httpdomain.py
index 5118e15..6c797d7 100644
--- a/sphinxcontrib/openapi/renderers/_httpdomain.py
+++ b/sphinxcontrib/openapi/renderers/_httpdomain.py
@@ -281,7 +281,7 @@ def render_operation(self, endpoint, method, operation):
         yield ""
 
         if operation.get("summary"):
-            yield f"   **{operation['summary']}**"
+            yield f"   **{' '.join(operation['summary'].split())}**"
             yield ""
 
         if operation.get("description"):
diff --git a/tests/renderers/httpdomain/test_render_operation.py b/tests/renderers/httpdomain/test_render_operation.py
index 4855d00..e95093f 100644
--- a/tests/renderers/httpdomain/test_render_operation.py
+++ b/tests/renderers/httpdomain/test_render_operation.py
@@ -108,6 +108,59 @@ def test_render_operation_summary(testrenderer, oas_fragment):
         """.rstrip())
 
 
+def test_render_operation_summary_block_scalar(testrenderer, oas_fragment):
+    """Operation's 'summary' is stripped of its trailing newline."""
+
+    markup = textify(
+        testrenderer.render_operation(
+            "/evidences",
+            "post",
+            oas_fragment("""
+                summary: |
+                  Create an evidence.
+                responses:
+                  '201':
+                    description: An evidence created.
+                """),
+        )
+    )
+    assert markup == textwrap.dedent("""\
+        .. http:post:: /evidences
+
+           **Create an evidence.**
+
+           :statuscode 201:
+              An evidence created.
+        """.rstrip())
+
+
+def test_render_operation_summary_multiline(testrenderer, oas_fragment):
+    """Operation's 'summary' is rendered as a single line."""
+
+    markup = textify(
+        testrenderer.render_operation(
+            "/evidences",
+            "post",
+            oas_fragment("""
+                summary: |
+                  Create
+                  an evidence.
+                responses:
+                  '201':
+                    description: An evidence created.
+                """),
+        )
+    )
+    assert markup == textwrap.dedent("""\
+        .. http:post:: /evidences
+
+           **Create an evidence.**
+
+           :statuscode 201:
+              An evidence created.
+        """.rstrip())
+
+
 def test_render_operation_description(testrenderer, oas_fragment):
     """Operation's 'description' is rendered."""