diff --git a/Makefile.ac b/Makefile.ac
index 6ff732697c..fc4d70cbce 100644
--- a/Makefile.ac
+++ b/Makefile.ac
@@ -61,7 +61,7 @@ NPROCS := 1
 J ?= AUTO
 ifeq ($J,AUTO)
 ifeq ($(UNAME),Linux)
-	NPROCS := $(shell grep -c ^processor /proc/cpuinfo)
+	NPROCS := $(shell grep -c '^processor' /proc/cpuinfo)
 else ifeq ($(UNAME),Darwin)
 	NPROCS := $(shell sysctl hw.ncpu | awk '{print $$2}')
 endif # $(UNAME)
diff --git a/conf/boards/chimera_1.0.makefile b/conf/boards/chimera_1.0.makefile
index 2275c2909c..92ad488d8c 100644
--- a/conf/boards/chimera_1.0.makefile
+++ b/conf/boards/chimera_1.0.makefile
@@ -21,7 +21,7 @@ MCU=cortex-m7
 USE_FPU=softfp
 USE_FPU_OPT= -mfpu=fpv5-d16
 
-USE_LTO=yes
+USE_LTO ?= yes
 
 $(TARGET).CFLAGS += -DSTM32F7 -DPPRZLINK_ENABLE_FD -DUSE_HARD_FAULT_RECOVERY
 
diff --git a/conf/boards/tawaki_common.makefile b/conf/boards/tawaki_common.makefile
index a7092a7250..5b685e0d52 100644
--- a/conf/boards/tawaki_common.makefile
+++ b/conf/boards/tawaki_common.makefile
@@ -20,7 +20,7 @@ MCU=cortex-m7
 USE_FPU=softfp
 USE_FPU_OPT= -mfpu=fpv5-d16
 
-USE_LTO=yes
+USE_LTO ?= yes
 
 $(TARGET).CFLAGS += -DSTM32F7 -DPPRZLINK_ENABLE_FD -DUSE_HARD_FAULT_RECOVERY