diff --git a/src/sgxenv.mk b/src/sgxenv.mk
index 469395d7..c4d96ae1 100644
--- a/src/sgxenv.mk
+++ b/src/sgxenv.mk
@@ -22,7 +22,7 @@ else ifeq ($(findstring -m32, $(CXXFLAGS)), -m32)
 	SGX_ARCH := x86
 endif
 
-SGX_COMMON_CFLAGS := -Wall
+SGX_COMMON_CFLAGS := -Wall -std=gnu11
 
 ifeq ($(SGX_ARCH), x86)
 	SGX_COMMON_CFLAGS += -m32
diff --git a/tools/docker/Dockerfile.centos7.2 b/tools/docker/Dockerfile.centos7.2
index daafe6a7..962a92ea 100644
--- a/tools/docker/Dockerfile.centos7.2
+++ b/tools/docker/Dockerfile.centos7.2
@@ -60,11 +60,12 @@ RUN git clone -b sgx_2.7.1_for_occlum https://github.com/occlum/linux-sgx && \
     rm -rf /tmp/linux-sgx
 
 # Install Rust
+ENV PATH="/root/.cargo/bin:$PATH"
 ENV OCCLUM_RUST_VERSION=nightly-2019-11-25
 RUN curl https://sh.rustup.rs -sSf | \
         sh -s -- --default-toolchain ${OCCLUM_RUST_VERSION} -y && \
-    rm -rf /root/.cargo/registry && rm -rf /root/.cargo/git
-ENV PATH="/root/.cargo/bin:$PATH"
+    rm -rf /root/.cargo/registry && rm -rf /root/.cargo/git && \
+    cargo -V
 
 # Upgrade gcc to compile occlum toolchain.
 # Use Developer Toolset 8 from Software Collections (SCLs) to have a newer gcc (8.3.1) than
diff --git a/tools/docker/Dockerfile.ubuntu16.04 b/tools/docker/Dockerfile.ubuntu16.04
index 2ab6dcb7..9f4383ad 100644
--- a/tools/docker/Dockerfile.ubuntu16.04
+++ b/tools/docker/Dockerfile.ubuntu16.04
@@ -60,11 +60,12 @@ RUN git clone -b sgx_2.7.1_for_occlum https://github.com/occlum/linux-sgx && \
     rm -rf /tmp/linux-sgx
 
 # Install Rust
+ENV PATH="/root/.cargo/bin:$PATH"
 ENV OCCLUM_RUST_VERSION=nightly-2019-11-25
 RUN curl https://sh.rustup.rs -sSf | \
         sh -s -- --default-toolchain ${OCCLUM_RUST_VERSION} -y && \
-    rm -rf /root/.cargo/registry && rm -rf /root/.cargo/git
-ENV PATH="/root/.cargo/bin:$PATH"
+    rm -rf /root/.cargo/registry && rm -rf /root/.cargo/git && \
+    cargo -V
 
 # Install Occlum toolchain
 COPY toolchains/gcc/* /tmp/
diff --git a/tools/docker/Dockerfile.ubuntu18.04 b/tools/docker/Dockerfile.ubuntu18.04
index 1eb8cbca..ed757dec 100644
--- a/tools/docker/Dockerfile.ubuntu18.04
+++ b/tools/docker/Dockerfile.ubuntu18.04
@@ -62,11 +62,12 @@ RUN git clone -b sgx_2.7.1_for_occlum https://github.com/occlum/linux-sgx && \
     rm -rf /tmp/linux-sgx
 
 # Install Rust
+ENV PATH="/root/.cargo/bin:$PATH"
 ENV OCCLUM_RUST_VERSION=nightly-2019-11-25
 RUN curl https://sh.rustup.rs -sSf | \
         sh -s -- --default-toolchain ${OCCLUM_RUST_VERSION} -y && \
-    rm -rf /root/.cargo/registry && rm -rf /root/.cargo/git
-ENV PATH="/root/.cargo/bin:$PATH"
+    rm -rf /root/.cargo/registry && rm -rf /root/.cargo/git && \
+    cargo -V
 
 # Install Occlum toolchain
 COPY toolchains/gcc/* /tmp/