diff --git a/boot/shim/shim.mk b/boot/shim/shim.mk
index 19b11f4086..ae57677320 100644
--- a/boot/shim/shim.mk
+++ b/boot/shim/shim.mk
@@ -13,10 +13,19 @@ SHIM_CPE_ID_VENDOR = redhat
 SHIM_INSTALL_TARGET = NO
 SHIM_INSTALL_IMAGES = YES
 
+SHIM_CFLAGS = $(TARGET_CFLAGS)
 SHIM_MAKE_OPTS = \
 	ARCH="$(GNU_EFI_PLATFORM)" \
 	CROSS_COMPILE="$(TARGET_CROSS)" \
-	DASHJ="-j$(PARALLEL_JOBS)"
+	DASHJ="-j$(PARALLEL_JOBS)" \
+	OPTIMIZATIONS="$(SHIM_CFLAGS)"
+
+# shim has some assembly function that is not present in Thumb mode:
+# Error: selected processor does not support `mrc p15,0,r2,c9,c13,0' in Thumb mode
+# so, we desactivate Thumb mode
+ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB),y)
+SHIM_CFLAGS += -marm
+endif
 
 define SHIM_BUILD_CMDS
 	$(TARGET_CONFIGURE_OPTS) $(MAKE) -C $(@D) $(SHIM_MAKE_OPTS)