diff --git a/mistralclient/api/v2/executions.py b/mistralclient/api/v2/executions.py
index e95c3789..7db0aec6 100644
--- a/mistralclient/api/v2/executions.py
+++ b/mistralclient/api/v2/executions.py
@@ -117,7 +117,8 @@ class ExecutionManager(base.ResourceManager):
         self._ensure_not_empty(id=id)
         qparams = {}
 
-        qparams['force'] = bool(force)
+        if force:
+            qparams['force'] = True
 
         query_string = ("?%s" % urlparse.urlencode(list(qparams.items()))
                         if qparams else "")
diff --git a/mistralclient/tests/functional/cli/v2/base_v2.py b/mistralclient/tests/functional/cli/v2/base_v2.py
index 4f0d69ca..f76679c3 100644
--- a/mistralclient/tests/functional/cli/v2/base_v2.py
+++ b/mistralclient/tests/functional/cli/v2/base_v2.py
@@ -245,7 +245,7 @@ class MistralClientTestBase(base.MistralCLIAuth, base.MistralCLIAltAuth):
             self.mistral_cli,
             admin,
             'execution-delete',
-            params=exec_id
+            params="{} --force".format(exec_id)
         )
 
         return ex
diff --git a/mistralclient/tests/functional/cli/v2/cli_tests_v2.py b/mistralclient/tests/functional/cli/v2/cli_tests_v2.py
index 2b7c8cca..befe02cc 100644
--- a/mistralclient/tests/functional/cli/v2/cli_tests_v2.py
+++ b/mistralclient/tests/functional/cli/v2/cli_tests_v2.py
@@ -660,7 +660,8 @@ class ExecutionCLITests(base_v2.MistralClientTestBase):
         self.assertIn(wf_name, [ex['Workflow name'] for ex in execs])
         self.assertIn(namespace, [ex['Workflow namespace'] for ex in execs])
 
-        self.mistral_admin('execution-delete', params=exec_id)
+        params = "{} --force".format(exec_id)
+        self.mistral_admin('execution-delete', params=params)
 
     def test_execution_create_delete(self):
 
@@ -688,7 +689,8 @@ class ExecutionCLITests(base_v2.MistralClientTestBase):
         self.assertIn(exec_id, [ex['ID'] for ex in execs])
         self.assertIn(wf_name, [ex['Workflow name'] for ex in execs])
 
-        self.mistral_admin('execution-delete', params=exec_id)
+        params = "{} --force".format(exec_id)
+        self.mistral_admin('execution-delete', params=params)
 
     def test_execution_create_with_input_and_start_task(self):
         execution = self.execution_create(
diff --git a/releasenotes/notes/fix-regression-with-execution-force-delete-af8d1968cb2673ef.yaml b/releasenotes/notes/fix-regression-with-execution-force-delete-af8d1968cb2673ef.yaml
new file mode 100644
index 00000000..4dca33b5
--- /dev/null
+++ b/releasenotes/notes/fix-regression-with-execution-force-delete-af8d1968cb2673ef.yaml
@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    mistralclient 3.5.0 introduced a new --force option to delete executions
+    that are still running. However, this had the unintended impact of passing
+    force=false when it wasn't provided. This is incompatible with previous
+    releases of the Mistral API which reject requests as they don't recognise
+    "force".