diff --git a/Dockerfile.dev b/Dockerfile.dev
index bdc5be42da..47475e34fc 100644
--- a/Dockerfile.dev
+++ b/Dockerfile.dev
@@ -12,6 +12,9 @@ ENV GOEXPERIMENT=greenteagc
 WORKDIR /build
 
 ADD go.mod go.sum ./
+# relaykit is a local submodule referenced via replace; its go.mod must be
+# present for go mod download to resolve the main module graph.
+ADD relaykit/go.mod ./relaykit/go.mod
 RUN go mod download
 
 COPY . .