diff --git a/.gitea/workflows/dotnet-build-test-postgres.yaml b/.gitea/workflows/dotnet-build-test-postgres.yaml
index d08c2ab..b3bee4c 100644
--- a/.gitea/workflows/dotnet-build-test-postgres.yaml
+++ b/.gitea/workflows/dotnet-build-test-postgres.yaml
@@ -18,11 +18,12 @@ on:
         required: false
         default: "Release"
         type: string
+      # string, not boolean: act_runner mangles boolean defaults (format() yields '%!t(string=false)').
       warnaserror:
-        description: "Treat build warnings as errors"
+        description: "Treat build warnings as errors (\"true\"/\"false\")"
         required: false
-        default: true
-        type: boolean
+        default: "true"
+        type: string
       working-directory:
         description: "Path where dotnet commands are executed (relative to repo root)"
         required: false
@@ -100,9 +101,10 @@ jobs:
       - name: Build
         run: |
           ARGS=(-c "$CONFIGURATION" --no-restore)
-          if [ "$WARNASERROR" = "true" ]; then
+          if [ "${WARNASERROR,,}" != "false" ]; then
             ARGS+=(-warnaserror)
           fi
+          set -x
           dotnet build ${SOLUTION:+"$SOLUTION"} "${ARGS[@]}"
 
       # The image's init phase listens on the unix socket only, so an open TCP port means the final server is up.
diff --git a/.gitea/workflows/dotnet-build-test.yaml b/.gitea/workflows/dotnet-build-test.yaml
index 2fd7731..ccee438 100644
--- a/.gitea/workflows/dotnet-build-test.yaml
+++ b/.gitea/workflows/dotnet-build-test.yaml
@@ -18,11 +18,12 @@ on:
         required: false
         default: "Release"
         type: string
+      # string, not boolean: act_runner mangles boolean defaults (format() yields '%!t(string=false)').
       warnaserror:
-        description: "Treat build warnings as errors"
+        description: "Treat build warnings as errors (\"true\"/\"false\")"
         required: false
-        default: true
-        type: boolean
+        default: "true"
+        type: string
       working-directory:
         description: "Path where dotnet commands are executed (relative to repo root)"
         required: false
@@ -65,9 +66,10 @@ jobs:
       - name: Build
         run: |
           ARGS=(-c "$CONFIGURATION" --no-restore)
-          if [ "$WARNASERROR" = "true" ]; then
+          if [ "${WARNASERROR,,}" != "false" ]; then
             ARGS+=(-warnaserror)
           fi
+          set -x
           dotnet build ${SOLUTION:+"$SOLUTION"} "${ARGS[@]}"
 
       - name: Test
diff --git a/README.md b/README.md
index 96b79f2..313641a 100644
--- a/README.md
+++ b/README.md
@@ -27,7 +27,7 @@ jobs:
 | `solution` | `""` | Solution/project file, relative to `working-directory`. If empty, dotnet uses the single sln/proj in that directory. |
 | `dotnet-version` | `10.0.x` | .NET SDK version |
 | `configuration` | `Release` | Build configuration |
-| `warnaserror` | `true` | Pass `-warnaserror` to `dotnet build` |
+| `warnaserror` | `"true"` | Pass `-warnaserror` to `dotnet build` unless the value is `"false"` |
 | `working-directory` | `.` | Where dotnet commands run |
 | `test-filter` | `""` | Optional `dotnet test --filter` expression |