diff --git a/rustup/Dockerfile b/rustup/Dockerfile
index 50ef5af..72207d0 100644
--- a/rustup/Dockerfile
+++ b/rustup/Dockerfile
@@ -30,7 +30,7 @@ RUN curl https://sh.rustup.rs -sSf | \
 ENV PATH=/root/.cargo/bin:$PATH
 
 ARG EXTRA=""
-RUN declare -a ARR=($EXTRA); for name in $ARR; do rustup install $name; done
+RUN ["/bin/bash", "-c", "declare -a ARR=($EXTRA); for name in $ARR; do rustup install $name; done"]
 
 ARG TARGETS=""
-RUN declare -a ARR=($TARGETS); for name in $ARR; do rustup target add $name; done
+RUN ["/bin/bash", "-c", "declare -a ARR=($TARGETS); for name in $ARR; do rustup target add $name; done"]