diff --git a/Dockerfile b/Dockerfile
index abf518997..7ace5ea1b 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -21,6 +21,7 @@ RUN AVAILABLE_TERRAFORM_VERSIONS="0.11.15 0.12.31 0.13.7 0.14.11 0.15.5 1.0.11 $
         "linux/amd64") TERRAFORM_ARCH=amd64 ;; \
         "linux/arm64") TERRAFORM_ARCH=arm64 ;; \
         "linux/arm/v7") TERRAFORM_ARCH=arm ;; \
+        *) echo "ERROR: 'TARGETPLATFORM' value expected: ${TARGETPLATFORM}"; exit 1 ;; \
     esac && \
     for VERSION in ${AVAILABLE_TERRAFORM_VERSIONS}; do \
         curl -LOs https://releases.hashicorp.com/terraform/${VERSION}/terraform_${VERSION}_linux_${TERRAFORM_ARCH}.zip && \