diff --git a/ChangeLog b/ChangeLog
index 3f8d553..71aa605 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -5,9 +5,15 @@
 Bugfix
    * Fix bug in mbedtls_mpi_add_mpi() that caused wrong results when the three
      arguments where the same (in-place doubling). Found and fixed by Janos
-     Follath.
+     Follath. #309
    * Fix potential build failures related to the 'apidoc' target, introduced
      in the previous patch release. Found by Robert Scheck. #390 #391
+   * Fix issue in Makefile that prevented building using armar. #386
+
+Changes
+   * On ARM platforms, when compiling with -O0 with GCC, Clang or armcc5,
+     don't use the optimized assembly for bignum multiplication. This removes
+     the need to pass -fomit-frame-pointer to avoid a build error with -O0.
 
 = mbed TLS 2.2.1 released 2016-01-05
 
diff --git a/include/mbedtls/bn_mul.h b/include/mbedtls/bn_mul.h
index 5408d41..1fc7aa6 100644
--- a/include/mbedtls/bn_mul.h
+++ b/include/mbedtls/bn_mul.h
@@ -563,7 +563,23 @@
 
 #endif /* TriCore */
 
-#if defined(__arm__)
+/*
+ * gcc -O0 by default uses r7 for the frame pointer, so it complains about our
+ * use of r7 below, unless -fomit-frame-pointer is passed. Unfortunately,
+ * passing that option is not easy when building with yotta.
+ *
+ * On the other hand, -fomit-frame-pointer is implied by any -Ox options with
+ * x !=0, which we can detect using __OPTIMIZE__ (which is also defined by
+ * clang and armcc5 under the same conditions).
+ *
+ * So, only use the optimized assembly below for optimized build, which avoids
+ * the build error and is pretty reasonable anyway.
+ */
+#if defined(__GNUC__) && !defined(__OPTIMIZE__)
+#define MULADDC_CANNOT_USE_R7
+#endif
+
+#if defined(__arm__) && !defined(MULADDC_CANNOT_USE_R7)
 
 #if defined(__thumb__) && !defined(__thumb2__)
 
diff --git a/library/Makefile b/library/Makefile
index 7d25343..00528b3 100644
--- a/library/Makefile
+++ b/library/Makefile
@@ -90,9 +90,9 @@
 # tls
 libmbedtls.a: $(OBJS_TLS)
 	echo "  AR    $@"
-	$(AR) rc $@ $(OBJS_TLS)
+	$(AR) -rc $@ $(OBJS_TLS)
 	echo "  RL    $@"
-	$(AR) s $@
+	$(AR) -s $@
 
 libmbedtls.$(SOEXT_TLS): $(OBJS_TLS) libmbedx509.so
 	echo "  LD    $@"
@@ -113,9 +113,9 @@
 # x509
 libmbedx509.a: $(OBJS_X509)
 	echo "  AR    $@"
-	$(AR) rc $@ $(OBJS_X509)
+	$(AR) -rc $@ $(OBJS_X509)
 	echo "  RL    $@"
-	$(AR) s $@
+	$(AR) -s $@
 
 libmbedx509.$(SOEXT_X509): $(OBJS_X509) libmbedcrypto.so
 	echo "  LD    $@"
@@ -136,9 +136,9 @@
 # crypto
 libmbedcrypto.a: $(OBJS_CRYPTO)
 	echo "  AR    $@"
-	$(AR) rc $@ $(OBJS_CRYPTO)
+	$(AR) -rc $@ $(OBJS_CRYPTO)
 	echo "  RL    $@"
-	$(AR) s $@
+	$(AR) -s $@
 
 libmbedcrypto.$(SOEXT_CRYPTO): $(OBJS_CRYPTO)
 	echo "  LD    $@"
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 9d3a38b..2f716bb 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -248,7 +248,7 @@
 scripts/config.pl unset MBEDTLS_THREADING_C
 scripts/config.pl unset MBEDTLS_MEMORY_BACKTRACE # execinfo.h
 scripts/config.pl unset MBEDTLS_MEMORY_BUFFER_ALLOC_C # calls exit
-CC=armcc WARNING_CFLAGS= make lib 2> armcc.stderr
+CC=armcc AR=armar WARNING_CFLAGS= make lib 2> armcc.stderr
 if [ -s armcc.stderr ]; then
     cat armcc.stderr
     exit 1;
diff --git a/tests/scripts/yotta-build.sh b/tests/scripts/yotta-build.sh
index 0651bae..19cc576 100755
--- a/tests/scripts/yotta-build.sh
+++ b/tests/scripts/yotta-build.sh
@@ -11,8 +11,12 @@
 yotta_build()
 {
     TARGET=$1
-    echo; echo "*** $TARGET ***"
+
+    echo; echo "*** $TARGET (release) ***"
     yt -t $TARGET build
+
+    echo; echo "*** $TARGET (debug) ***"
+    yt -t $TARGET build -d
 }
 
 if uname -a | grep 'Linux.*x86' >/dev/null; then