diff --git a/arscan.c b/arscan.c
index 6bc5af24..f4978486 100644
--- a/arscan.c
+++ b/arscan.c
@@ -137,8 +137,8 @@ VMS_get_member_info(struct dsc$descriptor_s *module, unsigned long *rfa)
 
 #ifdef TEST
   /* When testing this code, it is useful to know the length returned */
-  printf("Input length = %d, actual = %d\n",
-      bufdesc.dsc$w_length, buffer_length);
+  printf ("Input length = %d, actual = %u\n",
+          bufdesc.dsc$w_length, buffer_length);
 #endif
 
   /* Conversion from VMS time to C time.
diff --git a/hash.c b/hash.c
index 7b4b2715..ed4c8766 100644
--- a/hash.c
+++ b/hash.c
@@ -277,10 +277,10 @@ void
 hash_print_stats (struct hash_table *ht, FILE *out_FILE)
 {
   /* GKM FIXME: honor NO_FLOAT */
-  fprintf (out_FILE, _("Load=%ld/%ld=%.0f%%, "), ht->ht_fill, ht->ht_size,
+  fprintf (out_FILE, _("Load=%lu/%lu=%.0f%%, "), ht->ht_fill, ht->ht_size,
 	   100.0 * (double) ht->ht_fill / (double) ht->ht_size);
-  fprintf (out_FILE, _("Rehash=%d, "), ht->ht_rehashes);
-  fprintf (out_FILE, _("Collisions=%ld/%ld=%.0f%%"), ht->ht_collisions, ht->ht_lookups,
+  fprintf (out_FILE, _("Rehash=%u, "), ht->ht_rehashes);
+  fprintf (out_FILE, _("Collisions=%lu/%lu=%.0f%%"), ht->ht_collisions, ht->ht_lookups,
 	   (ht->ht_lookups
 	    ? (100.0 * (double) ht->ht_collisions / (double) ht->ht_lookups)
 	    : 0));
diff --git a/maintMakefile b/maintMakefile
index a275b88c..cab8dd6a 100644
--- a/maintMakefile
+++ b/maintMakefile
@@ -20,7 +20,14 @@ GNUWEBDIR ?= $(SRCROOTDIR)/gnu-www
 MAKEWEBDIR ?= $(SRCROOTDIR)/make/make-web
 
 # We like mondo-warnings!
-AM_CFLAGS += -Wall -Wwrite-strings -Wextra -Wdeclaration-after-statement -Wshadow -Wpointer-arith -Wbad-function-cast
+AM_CFLAGS += -Wall -Wextra -Werror -Wwrite-strings -Wshadow -Wpointer-arith \
+	-Wdeclaration-after-statement -Wbad-function-cast -Wformat-security \
+	-Wtype-limits -Wunused-but-set-parameter -Wlogical-op \
+	-Wignored-qualifiers -Wformat-signedness -Wduplicated-cond
+
+# Unfortunately the Guile headers are sometimes broken.  Convince GCC
+# to treat them as system headers so warnings are ignored.
+GUILE_CFLAGS := $(patsubst -I%,-isystem %,$(GUILE_CFLAGS))
 
 MAKE_MAINTAINER_MODE := -DMAKE_MAINTAINER_MODE
 AM_CPPFLAGS += $(MAKE_MAINTAINER_MODE)