diff --git a/Makefile.ac b/Makefile.ac
index b2f40075c6..0b61ff8c95 100644
--- a/Makefile.ac
+++ b/Makefile.ac
@@ -56,6 +56,20 @@ else
 	MKTEMP = mktemp
 endif
 
+# detection of number of processors for parallel compilation
+# can be overridden by calling toplevel make with e.g. J=2
+NPROCS := 1
+ifeq ($J,)
+ifeq ($(UNAME),Linux)
+  NPROCS := $(shell grep -c ^processor /proc/cpuinfo)
+else ifeq ($(UNAME),Darwin)
+  NPROCS := $(shell sysctl hw.ncpu | awk '{print $$2}')
+endif # $(UNAME)
+else
+  NPROCS := $J
+endif # $J
+
+
 # "make Q=''" to get full echo
 Q=@
 
@@ -176,8 +190,8 @@ $(SETTINGS_TELEMETRY) : $(PERIODIC_H)
 	@echo BUILD $(AIRCRAFT), TARGET $*
 	$(Q)PAPARAZZI_SRC=$(PAPARAZZI_SRC) PAPARAZZI_HOME=$(PAPARAZZI_HOME) TARGET=$* Q=$(Q) $(GENERATORS)/gen_aircraft.out $(AIRCRAFT)
 
-%.compile: %.ac_h print_version
-	cd $(AIRBORNE); $(MAKE) TARGET=$* all
+%.compile: %.ac_h | print_version
+	cd $(AIRBORNE); $(MAKE) -j$(NPROCS) TARGET=$* all
 
 %.upload: %.compile
 	cd $(AIRBORNE); $(MAKE) TARGET=$* upload
diff --git a/conf/Makefile.lpc21 b/conf/Makefile.lpc21
index 7313b7c2c9..64205059b6 100644
--- a/conf/Makefile.lpc21
+++ b/conf/Makefile.lpc21
@@ -173,6 +173,11 @@ include $(PAPARAZZI_SRC)/conf/Makefile.arm-embedded-common
 # Default target.
 all: printcommands sizebefore build sizeafter
 
+# depend order only for parallel make
+sizebefore: | printcommands
+build: | printcommands sizebefore
+sizeafter: | build
+
 build: $(OBJDIR) elf hex lss sym
 
 $(OBJDIR):
diff --git a/conf/Makefile.omap b/conf/Makefile.omap
index da5e15c86d..4e5fedcc8c 100644
--- a/conf/Makefile.omap
+++ b/conf/Makefile.omap
@@ -79,6 +79,9 @@ printcommands:
 
 all: printcommands build
 
+# depend order only for parallel make
+build: | printcommands
+
 build: $(OBJDIR) elf
 
 $(OBJDIR):
diff --git a/conf/Makefile.stm32 b/conf/Makefile.stm32
index 4e8176523d..857d31941e 100644
--- a/conf/Makefile.stm32
+++ b/conf/Makefile.stm32
@@ -152,6 +152,11 @@ include $(PAPARAZZI_SRC)/conf/Makefile.arm-embedded-common
 # Default target.
 all: printcommands sizebefore build sizeafter
 
+# depend order only for parallel make
+sizebefore: | printcommands
+build: | printcommands sizebefore
+sizeafter: | build
+
 build: $(OBJDIR) elf bin hex
 # lss sym
 
@@ -189,7 +194,7 @@ sym: $(OBJDIR)/$(TARGET).sym
 # Link: create ELF output file from object files.
 .SECONDARY : $(OBJDIR)/$(TARGET).elf
 .PRECIOUS : $(COBJ) $(AOBJ)
-%.elf:  $(COBJ) $(AOBJ)
+%.elf: $(COBJ) $(AOBJ) | $(OBJDIR)
 	@echo LD $@
 	$(Q)$(LD) $(LDFLAGS) $($(TARGET).LDFLAGS) -o $@ $(COBJ) $(AOBJ) $(LDLIBS)
 
@@ -209,14 +214,12 @@ $(AOBJ) : $(OBJDIR)/%.o : %.S
 include $(PAPARAZZI_SRC)/conf/Makefile.stm32-upload
 
 # Listing of phony targets.
-.PHONY : all build elf bin lss sym start_gdb start_telnet
+.PHONY : all build elf bin lss sym
 
 #
 # Dependencies
 #
-
-DEPS = $(addprefix $(OBJDIR)/,$($(TARGET).srcs:.c=.d))
-
 ifneq ($(MAKECMDGOALS),clean)
+DEPS = $(addprefix $(OBJDIR)/,$($(TARGET).srcs:.c=.d))
 -include $(DEPS)
 endif