diff --git a/Dockerfile b/Dockerfile
index b2c1a028a..1cae15c74 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,7 +1,20 @@
-# Container for building Go binary.
-FROM golang:1.27.3-trixie AS builder
-# Install dependencies
-RUN apt-get update && apt-get install -y --no-install-recommends build-essential git
+# Container for building Go binary. It always runs on the build platform and
+# cross-compiles for the target platform, so multi-platform builds don't compile
+# under QEMU emulation.
+FROM --platform=$BUILDPLATFORM golang:1.27.3-trixie AS builder
+ARG BUILDARCH
+ARG TARGETOS
+ARG TARGETARCH
+# Install dependencies, plus a cgo cross compiler when the target arch differs
+# from the build arch (herumi bls requires cgo).
+RUN apt-get update && apt-get install -y --no-install-recommends build-essential git \
+  && if [ "$TARGETARCH" != "$BUILDARCH" ]; then \
+    case "$TARGETARCH" in \
+      arm64) apt-get install -y --no-install-recommends gcc-aarch64-linux-gnu libc6-dev-arm64-cross ;; \
+      amd64) apt-get install -y --no-install-recommends gcc-x86-64-linux-gnu libc6-dev-amd64-cross ;; \
+      *) echo "unsupported TARGETARCH=$TARGETARCH" && exit 1 ;; \
+    esac; \
+  fi
 
 # Prep and copy source
 WORKDIR /app/charon
@@ -11,14 +24,20 @@ COPY . .
 # Populate GO_BUILD_FLAG with a build arg to provide an optional go build flag.
 ARG GO_BUILD_FLAG
 ENV GO_BUILD_FLAG=${GO_BUILD_FLAG}
-RUN echo "Building with GO_BUILD_FLAG='${GO_BUILD_FLAG}'"
+RUN echo "Building for ${TARGETOS}/${TARGETARCH} on ${BUILDARCH} with GO_BUILD_FLAG='${GO_BUILD_FLAG}'"
 
-# Build with Go module and Go build caches.
+# Build with Go module and Go build caches (the build cache keys entries by
+# GOARCH, so both target arches can share it).
 RUN \
   --mount=type=cache,target=/go/pkg \
   --mount=type=cache,target=/root/.cache/go-build \
-  go build -o charon "${GO_BUILD_FLAG}" .
-RUN echo "Built charon version=$(./charon version)"
+  if [ "$TARGETARCH" != "$BUILDARCH" ]; then \
+    case "$TARGETARCH" in \
+      arm64) export CC=aarch64-linux-gnu-gcc ;; \
+      amd64) export CC=x86_64-linux-gnu-gcc ;; \
+    esac; \
+  fi \
+  && CGO_ENABLED=1 GOOS="$TARGETOS" GOARCH="$TARGETARCH" go build -o charon "${GO_BUILD_FLAG}" .
 
 # Copy final binary into light stage.
 FROM debian:trixie-slim
@@ -33,6 +52,9 @@ ARG GITHUB_SHA=local
 ENV GITHUB_SHA=${GITHUB_SHA}
 
 COPY --from=builder /app/charon/charon /usr/local/bin/
+# Sanity check the binary on the target platform (the builder can't run a
+# cross-compiled binary).
+RUN version="$(/usr/local/bin/charon version)" && echo "Built charon version=${version}"
 
 # Don't run container as root
 ENV USER=charon
diff --git a/testutil/promrated/Dockerfile b/testutil/promrated/Dockerfile
index 361867069..3d48e8442 100644
--- a/testutil/promrated/Dockerfile
+++ b/testutil/promrated/Dockerfile
@@ -1,14 +1,23 @@
-FROM golang:1.27.3-alpine AS builder
+# Build on the build platform and cross-compile for the target platform, so
+# multi-platform builds don't compile under QEMU emulation. promrated has no cgo
+# dependencies, so a pure Go build cross-compiles without a C toolchain.
+FROM --platform=$BUILDPLATFORM golang:1.27.3-alpine AS builder
 
-# Install dependencies
-RUN apk add --no-cache build-base git
+# Install dependencies (git for VCS build info)
+RUN apk add --no-cache git
 
 WORKDIR /app
 
 COPY . .
 
-# Build with Go module and Go build caches.
-RUN go build -o promrated github.com/obolnetwork/charon/testutil/promrated/promrated
+ARG TARGETOS
+ARG TARGETARCH
+RUN CGO_ENABLED=0 GOOS="$TARGETOS" GOARCH="$TARGETARCH" \
+  go build -o promrated github.com/obolnetwork/charon/testutil/promrated/promrated
+
+FROM alpine:3.24
+
+COPY --from=builder /app/promrated /app/promrated
 
 # Don't run container as root
 ENV USER=promrated