diff --git a/.cirrus.yml b/.cirrus.yml
index 61f094c2b..0039f8c07 100644
--- a/.cirrus.yml
+++ b/.cirrus.yml
@@ -141,7 +141,7 @@ rocky_task:
     LC_ALL: C
     CIRRUS_CLONE_DEPTH: 1
     USE_CONFIG: yes
-    CFLAGS: -std=gnu90 -Wformat -Wformat=2
+    CFLAGS: -g -O3 -std=gnu90 -Wformat -Wformat=2 -Wextra -Wno-sign-compare -Wno-unused-parameter -Wno-missing-field-initializers -Wno-empty-body
 
   # NB: we could consider building a docker image with these
   # preinstalled and specifying that instead, to speed up testing.
diff --git a/hts.c b/hts.c
index 42be3f21f..a4ae32a69 100644
--- a/hts.c
+++ b/hts.c
@@ -1322,7 +1322,7 @@ int hts_parse_opt_list(htsFormat *fmt, const char *str) {
  *        -1 on failure.
  */
 int hts_parse_format(htsFormat *format, const char *str) {
-    char fmt[8];
+    char fmt[9];
     const char *cp = scan_keyword(str, ',', fmt, sizeof fmt);
 
     format->version.minor = 0; // unknown
diff --git a/test/test-bcf-sr.c b/test/test-bcf-sr.c
index b4943b5ef..e24954685 100644
--- a/test/test-bcf-sr.c
+++ b/test/test-bcf-sr.c
@@ -179,6 +179,7 @@ int main(int argc, char *argv[])
                 break;
             case 'h':
                 usage(EXIT_SUCCESS);
+                // fall-through
             default: usage(EXIT_FAILURE);
         }
     }