diff --git a/Makefile b/Makefile
index 05f4d55..d7f5997 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,5 @@
 .PHONY: doc test bench
+.NOTPARALLEL: clean
 
 all:
 	${MAKE} -C src
diff --git a/src/Makefile b/src/Makefile
index 822ccfa..da0452d 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -10,6 +10,8 @@ P = match itoa
 A = ../lib/libpsyc.a
 SO = ../lib/libpsyc.so
 
+.NOTPARALLEL: clean
+
 all: CC := ${WRAPPER} ${CC}
 all: lib
 
@@ -21,13 +23,13 @@ diet: WRAPPER = ${DIET}
 diet: CC := ${WRAPPER} ${CC}
 diet: lib
 
-lib: $O $A ${SO}
+lib: $A ${SO}
 
-${SO}:
+${SO}: $O
 	@mkdir -p ../lib
 	${CC} ${CFLAGS} -shared -lm -o $@ $O
 
-$A:
+$A: $O
 	@mkdir -p ../lib
 	${WRAPPER} ${AR} rcs $@ $O