See https://github.com/curl/trurl/pull/158#issuecomment-1512397801.
--- a/Makefile
+++ b/Makefile
@@ -1,8 +1,6 @@
 TARGET = trurl
 OBJS = trurl.o
-LDLIBS != curl-config --libs
-CFLAGS != curl-config --cflags
-CFLAGS += -W -Wall -pedantic -g
+LDLIBS = $(shell curl-config --libs)
 MANUAL = trurl.1
 
 PREFIX ?= /usr/local
@@ -13,7 +11,7 @@ INSTALL ?= install
 PYTHON3 ?= python3
 
 $(TARGET): $(OBJS)
-	$(CC) $(OBJS) -o $(TARGET) $(LDLIBS) $(LDFLAGS)
+	$(CC) $(CPPFLAGS) $(CFLAGS) -Wall $(shell curl-config --cflags) $(LDFLAGS) $(OBJS) -o $(TARGET) $(LDLIBS)
 
 trurl.o:trurl.c version.h