diff --git a/conformance_tests.yaml b/conformance_tests.yaml
index 42a92557..ffc56074 100644
--- a/conformance_tests.yaml
+++ b/conformance_tests.yaml
@@ -3461,3 +3461,15 @@
     }
   }
   tags: [ required, command_line_tool ]
+
+- id: default_with_falsey_value
+  job: tests/empty.json
+  tool: tests/default_with_falsey_value.cwl
+  doc: Confirms that "false"-like (but not 'null') values override any default
+  output:
+    out:
+      class: File
+      basename: file.txt
+      size: 14
+      checksum: sha1$0074b1841ab5103cc0442f739d9fb41a33b602ee
+  tags: [ step_input, workflow ]
\ No newline at end of file
diff --git a/tests/default_with_falsey_value.cwl b/tests/default_with_falsey_value.cwl
new file mode 100644
index 00000000..28ea09fc
--- /dev/null
+++ b/tests/default_with_falsey_value.cwl
@@ -0,0 +1,39 @@
+cwlVersion: v1.0
+class: Workflow
+
+doc: reproduces https://github.com/DataBiosphere/toil/issues/3141
+
+requirements:
+  StepInputExpressionRequirement: {}
+
+inputs:
+  input_bool:
+    type: boolean
+    default: False
+
+outputs:
+  out:
+    type: File
+    outputSource: echo/out
+
+steps:
+  echo:
+    run:
+      cwlVersion: v1.0
+      class: CommandLineTool
+      baseCommand: echo
+      inputs:
+        str:
+          type: string
+          default: "UNDEFINED"
+          inputBinding:
+            position: 1
+      outputs:
+        out: stdout
+      stdout: file.txt
+    in:
+      str:
+        source: input_bool
+        valueFrom: self is $(self)
+    out:
+      - out