diff --git a/sam.c b/sam.c
index 878fcc270..dc8b9c183 100644
--- a/sam.c
+++ b/sam.c
@@ -3220,8 +3220,10 @@ int sam_format1(const bam_hdr_t *h, const bam1_t *b, kstring_t *str)
 // reference count the structure.
 int sam_write1(htsFile *fp, const sam_hdr_t *hdr, const bam1_t *b)
 {
-    const sam_hdr_t *h = hdr;
-    if (!h) h = fp->bam_header;
+    if (!fp || !b) { errno = EINVAL; return -1; }
+    const sam_hdr_t *h = hdr ? hdr : fp->bam_header;
+    if (!h) { hts_log_error("No header available for file \"%s\"", fp->fn); return -1; }
+
     switch (fp->format.format) {
     case binary_format:
         fp->format.category = sequence_data;
diff --git a/vcf.c b/vcf.c
index 8416c5e80..1905c7311 100644
--- a/vcf.c
+++ b/vcf.c
@@ -3296,7 +3296,11 @@ static int vcf_idx_init(htsFile *fp, bcf_hdr_t *h, int min_shift, const char *fn
         return -1;
     }
     fp->fnidx = strdup(fnidx);
-    if (!fp->fnidx) return -1;
+    if (!fp->fnidx) {
+        hts_idx_destroy(fp->idx);
+        fp->idx = NULL;
+        return -1;
+    }
 
     return 0;
 }
@@ -3317,7 +3321,11 @@ int bcf_idx_init(htsFile *fp, bcf_hdr_t *h, int min_shift, const char *fnidx) {
     fp->idx = hts_idx_init(nids, HTS_FMT_CSI, bgzf_tell(fp->fp.bgzf), min_shift, n_lvls);
     if (!fp->idx) return -1;
     fp->fnidx = strdup(fnidx);
-    if (!fp->fnidx) return -1;
+    if (!fp->fnidx) {
+        hts_idx_destroy(fp->idx);
+        fp->idx = NULL;
+        return -1;
+    }
 
     return 0;
 }