diff --git a/ChangeLog.d/armclang-compile-fix.txt b/ChangeLog.d/armclang-compile-fix.txt
new file mode 100644
index 0000000..93ad6af
--- /dev/null
+++ b/ChangeLog.d/armclang-compile-fix.txt
@@ -0,0 +1,5 @@
+Bugfix
+   * Fix clang and armclang compilation error when targeting certain Arm
+     M-class CPUs (Cortex-M0, Cortex-M0+, Cortex-M1, Cortex-M23,
+     SecurCore SC000). Fixes #1077.
+
diff --git a/include/mbedtls/bn_mul.h b/include/mbedtls/bn_mul.h
index a0bc4d0..6414e54 100644
--- a/include/mbedtls/bn_mul.h
+++ b/include/mbedtls/bn_mul.h
@@ -677,6 +677,15 @@
 #if defined(__arm__) && !defined(MULADDC_CANNOT_USE_R7)
 
 #if defined(__thumb__) && !defined(__thumb2__)
+#if !defined(__ARMCC_VERSION) && !defined(__clang__) \
+    && !defined(__llvm__) && !defined(__INTEL_COMPILER)
+/*
+ * Thumb 1 ISA. This code path has only been tested successfully on gcc;
+ * it does not compile on clang or armclang.
+ *
+ * Other compilers which define __GNUC__ may not work. The above macro
+ * attempts to exclude these untested compilers.
+ */
 
 #define MULADDC_INIT                                    \
     asm(                                                \
@@ -731,6 +740,8 @@
            "r6", "r7", "r8", "r9", "cc"         \
          );
 
+#endif /* Compiler is gcc */
+
 #elif (__ARM_ARCH >= 6) && \
     defined (__ARM_FEATURE_DSP) && (__ARM_FEATURE_DSP == 1)
 
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 87defc0..dae54c7 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -3156,6 +3156,25 @@
     not grep __aeabi_lmul library/*.o
 }
 
+component_build_arm_clang_thumb () {
+    # ~ 30s
+
+    scripts/config.py baremetal
+
+    msg "build: clang thumb 2, make"
+    make clean
+    make CC="clang" CFLAGS='-std=c99 -Werror -Os --target=arm-linux-gnueabihf -march=armv7-m -mthumb' lib
+
+    # Some Thumb 1 asm is sensitive to optimisation level, so test both -O0 and -Os
+    msg "build: clang thumb 1 -O0, make"
+    make clean
+    make CC="clang" CFLAGS='-std=c99 -Werror -O0 --target=arm-linux-gnueabihf -mcpu=arm1136j-s -mthumb' lib
+
+    msg "build: clang thumb 1 -Os, make"
+    make clean
+    make CC="clang" CFLAGS='-std=c99 -Werror -Os --target=arm-linux-gnueabihf -mcpu=arm1136j-s -mthumb' lib
+}
+
 component_build_armcc () {
     msg "build: ARM Compiler 5"
     scripts/config.py baremetal
@@ -3166,6 +3185,8 @@
 
     make clean
 
+    # Compile mostly with -O1 since some Arm inline assembly is disabled for -O0.
+
     # ARM Compiler 6 - Target ARMv7-A
     armc6_build_test "--target=arm-arm-none-eabi -march=armv7-a"
 
@@ -3180,7 +3201,14 @@
 
     # ARM Compiler 6 - Target ARMv8-A - AArch64
     armc6_build_test "--target=aarch64-arm-none-eabi -march=armv8.2-a"
+
+    # ARM Compiler 6 - Target Cortex-M0 - no optimisation
+    armc6_build_test "-O0 --target=arm-arm-none-eabi -mcpu=cortex-m0"
+
+    # ARM Compiler 6 - Target Cortex-M0
+    armc6_build_test "-Os --target=arm-arm-none-eabi -mcpu=cortex-m0"
 }
+
 support_build_armcc () {
     armc5_cc="$ARMC5_BIN_DIR/armcc"
     armc6_cc="$ARMC6_BIN_DIR/armclang"