diff --git a/qpkg/prereq.c b/qpkg/prereq.c
index b5962e6..b9e50e2 100644
--- a/qpkg/prereq.c
+++ b/qpkg/prereq.c
@@ -39,7 +39,9 @@ static struct pkg **installs = NULL;
 static int n_best;	/* undefined if best == NULL */
 static int n_install = 0;
 static int install_max = 0;
-static int debug = 0;
+
+
+/* ----- Version comparison ------------------------------------------------ */
 
 
 static int epoch(const char **s, const struct id *id)
@@ -100,6 +102,9 @@ static int comp_versions(const struct id *va, const struct id *vb)
 }
 
 
+/* ----- List of packages considered for installation ---------------------- */
+
+
 static void done(void)
 {
 	int size;
@@ -139,6 +144,9 @@ static void backtrack(void)
 }
 
 
+/* ----- Check dependencies and conflicts ---------------------------------- */
+
+
 static int satisfies(const struct pkg *pkg, const struct ref *ref)
 {
 	int cmp;
@@ -171,6 +179,9 @@ static int conflicts(const struct pkg *pkg, const struct list *conf)
 }
 
 
+/* ----- Recurse through lists and layers of dependencies ------------------ */
+
+
 static void print_debug(const struct pkg *pkg, const struct stack *top,
     int level)
 {
diff --git a/qpkg/qpkg.c b/qpkg/qpkg.c
index 0c331dc..76d6834 100644
--- a/qpkg/qpkg.c
+++ b/qpkg/qpkg.c
@@ -26,6 +26,8 @@
 struct tree *packages = NULL;
 struct tree *versions = NULL;
 
+int debug = 0;
+
 
 static void list_all_packages(void)
 {
@@ -115,8 +117,9 @@ static void find_prereq(const char *name, const char *version)
 static void usage(const char *name)
 {
 	fprintf(stderr,
-"usage: %s [pkg-list ...] list [pkg]\n"
-"       %s [pkg-list ...] prereq pkg [version]\n"
+"usage: %s options [pkg-list ...] list [pkg]\n"
+"       %s options [pkg-list ...] prereq pkg [version]\n\n"
+"  -d   enable debugging output\n"
     , name, name);
 	exit(1);
 }
@@ -133,6 +136,10 @@ int main(int argc, char **argv)
 		usage(*argv);
 
 	for (arg = 1; arg != argc; arg++) {
+		if (!strcmp(argv[arg], "-d")) {
+			debug = 1;
+			continue;
+		}
 		if (*argv[arg] == '-')
 			usage(*argv);
 		if (!strcmp(argv[arg], "list")) {
diff --git a/qpkg/qpkg.h b/qpkg/qpkg.h
index 62147c8..96e862e 100644
--- a/qpkg/qpkg.h
+++ b/qpkg/qpkg.h
@@ -52,4 +52,6 @@ struct pkg {
 struct tree *packages;
 struct tree *versions;
 
+int debug;
+
 #endif /* !QPKG_H */