diff --git a/misc/bstr.c b/misc/bstr.c
index 4a8bf16ac1..120abef8fe 100644
--- a/misc/bstr.c
+++ b/misc/bstr.c
@@ -376,17 +376,18 @@ void bstr_xappend(void *talloc_ctx, bstr *s, bstr append)
     s->start[s->len] = '\0';
 }
 
-void bstr_xappend_asprintf(void *talloc_ctx, bstr *s, const char *fmt, ...)
+int bstr_xappend_asprintf(void *talloc_ctx, bstr *s, const char *fmt, ...)
 {
     va_list ap;
     va_start(ap, fmt);
-    bstr_xappend_vasprintf(talloc_ctx, s, fmt, ap);
+    int ret = bstr_xappend_vasprintf(talloc_ctx, s, fmt, ap);
     va_end(ap);
+    return ret;
 }
 
 // Exactly as bstr_xappend(), but with a formatted string.
-void bstr_xappend_vasprintf(void *talloc_ctx, bstr *s, const char *fmt,
-                            va_list ap)
+int bstr_xappend_vasprintf(void *talloc_ctx, bstr *s, const char *fmt,
+                           va_list ap)
 {
     int size;
     va_list copy;
@@ -397,13 +398,14 @@ void bstr_xappend_vasprintf(void *talloc_ctx, bstr *s, const char *fmt,
     va_end(copy);
 
     if (size < 0)
-        abort();
+        return size;
 
     if (avail < 1 || size + 1 > avail) {
         resize_append(talloc_ctx, s, size + 1);
         vsnprintf(s->start + s->len, size + 1, fmt, ap);
     }
     s->len += size;
+    return size;
 }
 
 bool bstr_case_startswith(struct bstr s, struct bstr prefix)
diff --git a/misc/bstr.h b/misc/bstr.h
index 5cc124ec36..d279a3a088 100644
--- a/misc/bstr.h
+++ b/misc/bstr.h
@@ -136,9 +136,9 @@ static inline struct bstr bstr_getline(struct bstr str, struct bstr *rest)
 struct bstr bstr_strip_linebreaks(struct bstr str);
 
 void bstr_xappend(void *talloc_ctx, bstr *s, bstr append);
-void bstr_xappend_asprintf(void *talloc_ctx, bstr *s, const char *fmt, ...)
+int bstr_xappend_asprintf(void *talloc_ctx, bstr *s, const char *fmt, ...)
     PRINTF_ATTRIBUTE(3, 4);
-void bstr_xappend_vasprintf(void *talloc_ctx, bstr *s, const char *fmt, va_list va)
+int bstr_xappend_vasprintf(void *talloc_ctx, bstr *s, const char *fmt, va_list va)
     PRINTF_ATTRIBUTE(3, 0);
 
 // If s starts/ends with prefix, return true and return the rest of the string