diff --git a/Dockerfile b/Dockerfile
index 7777e9e..c877099 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,10 +1,12 @@
 # Static CGO-free binary; distroless/static brings CA certs and nothing else.
-FROM golang:1.27-trixie AS builder
+# Cross-compile on the runner's own arch; building arm64 under QEMU took minutes.
+FROM --platform=$BUILDPLATFORM golang:1.27-trixie AS builder
+ARG TARGETOS TARGETARCH
 WORKDIR /src
 COPY go.mod go.sum ./
 RUN go mod download
 COPY . .
-RUN CGO_ENABLED=0 go build -trimpath -ldflags="-s -w" -o /github-actions-runner-exporter .
+RUN CGO_ENABLED=0 GOOS=$TARGETOS GOARCH=$TARGETARCH go build -trimpath -ldflags="-s -w" -o /github-actions-runner-exporter .
 
 FROM gcr.io/distroless/static-debian13:nonroot
 COPY --from=builder /github-actions-runner-exporter /github-actions-runner-exporter