diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index ca73722ba..4fafe0208 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -1827,7 +1827,7 @@ component_test_no_64bit_multiplication () {
 component_build_arm_none_eabi_gcc () {
     msg "build: ${ARM_NONE_EABI_GCC_PREFIX}gcc -O1" # ~ 10s
     scripts/config.py baremetal
-    make CC="${ARM_NONE_EABI_GCC_PREFIX}gcc" AR="${ARM_NONE_EABI_GCC_PREFIX}ar" LD="${ARM_NONE_EABI_GCC_PREFIX}ld" CFLAGS='-Werror -Wall -Wextra -O1' lib
+    make CC="${ARM_NONE_EABI_GCC_PREFIX}gcc" AR="${ARM_NONE_EABI_GCC_PREFIX}ar" LD="${ARM_NONE_EABI_GCC_PREFIX}ld" CFLAGS='-std=c99 -Werror -Wall -Wextra -O1' lib
 
     msg "size: ${ARM_NONE_EABI_GCC_PREFIX}gcc -O1"
     ${ARM_NONE_EABI_GCC_PREFIX}size library/*.o
@@ -1841,7 +1841,7 @@ component_build_arm_none_eabi_gcc_arm5vte () {
     # See https://github.com/ARMmbed/mbedtls/pull/2169 and comments.
     # It would be better to build with arm-linux-gnueabi-gcc but
     # we don't have that on our CI at this time.
-    make CC="${ARM_NONE_EABI_GCC_PREFIX}gcc" AR="${ARM_NONE_EABI_GCC_PREFIX}ar" CFLAGS='-Werror -Wall -Wextra -march=armv5te -O1' LDFLAGS='-march=armv5te' SHELL='sh -x' lib
+    make CC="${ARM_NONE_EABI_GCC_PREFIX}gcc" AR="${ARM_NONE_EABI_GCC_PREFIX}ar" CFLAGS='-std=c99 -Werror -Wall -Wextra -march=armv5te -O1' LDFLAGS='-march=armv5te' SHELL='sh -x' lib
 
     msg "size: ${ARM_NONE_EABI_GCC_PREFIX}gcc -march=armv5te -O1"
     ${ARM_NONE_EABI_GCC_PREFIX}size library/*.o
@@ -1850,7 +1850,7 @@ component_build_arm_none_eabi_gcc_arm5vte () {
 component_build_arm_none_eabi_gcc_m0plus () {
     msg "build: ${ARM_NONE_EABI_GCC_PREFIX}gcc -mthumb -mcpu=cortex-m0plus" # ~ 10s
     scripts/config.py baremetal
-    make CC="${ARM_NONE_EABI_GCC_PREFIX}gcc" AR="${ARM_NONE_EABI_GCC_PREFIX}ar" LD="${ARM_NONE_EABI_GCC_PREFIX}ld" CFLAGS='-Werror -Wall -Wextra -mthumb -mcpu=cortex-m0plus -Os' lib
+    make CC="${ARM_NONE_EABI_GCC_PREFIX}gcc" AR="${ARM_NONE_EABI_GCC_PREFIX}ar" LD="${ARM_NONE_EABI_GCC_PREFIX}ld" CFLAGS='-std=c99 -Werror -Wall -Wextra -mthumb -mcpu=cortex-m0plus -Os' lib
 
     msg "size: ${ARM_NONE_EABI_GCC_PREFIX}gcc -mthumb -mcpu=cortex-m0plus -Os"
     ${ARM_NONE_EABI_GCC_PREFIX}size library/*.o
@@ -1860,7 +1860,7 @@ component_build_arm_none_eabi_gcc_no_udbl_division () {
     msg "build: ${ARM_NONE_EABI_GCC_PREFIX}gcc -DMBEDTLS_NO_UDBL_DIVISION, make" # ~ 10s
     scripts/config.py baremetal
     scripts/config.py set MBEDTLS_NO_UDBL_DIVISION
-    make CC="${ARM_NONE_EABI_GCC_PREFIX}gcc" AR="${ARM_NONE_EABI_GCC_PREFIX}ar" LD="${ARM_NONE_EABI_GCC_PREFIX}ld" CFLAGS='-Werror -Wall -Wextra' lib
+    make CC="${ARM_NONE_EABI_GCC_PREFIX}gcc" AR="${ARM_NONE_EABI_GCC_PREFIX}ar" LD="${ARM_NONE_EABI_GCC_PREFIX}ld" CFLAGS='-std=c99 -Werror -Wall -Wextra' lib
     echo "Checking that software 64-bit division is not required"
     if_build_succeeded not grep __aeabi_uldiv library/*.o
 }
@@ -1869,7 +1869,7 @@ component_build_arm_none_eabi_gcc_no_64bit_multiplication () {
     msg "build: ${ARM_NONE_EABI_GCC_PREFIX}gcc MBEDTLS_NO_64BIT_MULTIPLICATION, make" # ~ 10s
     scripts/config.py baremetal
     scripts/config.py set MBEDTLS_NO_64BIT_MULTIPLICATION
-    make CC="${ARM_NONE_EABI_GCC_PREFIX}gcc" AR="${ARM_NONE_EABI_GCC_PREFIX}ar" LD="${ARM_NONE_EABI_GCC_PREFIX}ld" CFLAGS='-Werror -O1 -march=armv6-m -mthumb' lib
+    make CC="${ARM_NONE_EABI_GCC_PREFIX}gcc" AR="${ARM_NONE_EABI_GCC_PREFIX}ar" LD="${ARM_NONE_EABI_GCC_PREFIX}ld" CFLAGS='-std=c99 -Werror -O1 -march=armv6-m -mthumb' lib
     echo "Checking that software 64-bit multiplication is not required"
     if_build_succeeded not grep __aeabi_lmul library/*.o
 }