diff --git a/src/LiveRecorder.WebApi/Dockerfile b/src/LiveRecorder.WebApi/Dockerfile
index c355119..91fd44e 100644
--- a/src/LiveRecorder.WebApi/Dockerfile
+++ b/src/LiveRecorder.WebApi/Dockerfile
@@ -24,7 +24,11 @@ ENV HTTP_PROXY=${HTTP_PROXY} \
 # resolve to the correct platform. Framework-dependent output — apphost stays
 # at /p:UseAppHost=false.
 ARG TARGETARCH
-RUN DOTNET_RID=$(case "$TARGETARCH" in amd64) echo linux-x64 ;; arm64) echo linux-arm64 ;; *) echo "unknown: $TARGETARCH" >&2; exit 1 ;; esac) ; \
+RUN case "$TARGETARCH" in \
+      amd64) DOTNET_RID=linux-x64 ;; \
+      arm64) DOTNET_RID=linux-arm64 ;; \
+      *) echo "ERROR: unknown TARGETARCH=$TARGETARCH" >&2; exit 1 ;; \
+    esac ; \
     echo "Building for TARGETARCH=$TARGETARCH -> RID=$DOTNET_RID"
 
 COPY . .