diff --git a/include/git2/commit.h b/include/git2/commit.h
index 4cc637466..692b3bdd9 100644
--- a/include/git2/commit.h
+++ b/include/git2/commit.h
@@ -255,7 +255,8 @@ GIT_EXTERN(int) git_commit_nth_gen_ancestor(
 /**
  * Get an arbitrary header field
  *
- * @param out the buffer to fill
+ * @param out the buffer to fill; existing content will be
+ * overwritten
  * @param commit the commit to look in
  * @param field the header field to return
  * @return 0 on succeess, GIT_ENOTFOUND if the field does not exist,
@@ -270,8 +271,10 @@ GIT_EXTERN(int) git_commit_header_field(git_buf *out, const git_commit *commit,
  * `GITERR_INVALID`. If the commit does not have a signature, the
  * error class will be `GITERR_OBJECT`.
  *
- * @param signature the signature block
- * @param signed_data signed data; this is the commit contents minus the signature block
+ * @param signature the signature block; existing content will be
+ * overwritten
+ * @param signed_data signed data; this is the commit contents minus the signature block;
+ * existing content will be overwritten
  * @param repo the repository in which the commit exists
  * @param commit_id the commit from which to extract the data
  * @param field the name of the header field containing the signature
diff --git a/src/buffer.h b/src/buffer.h
index cdfca6d99..a76b2d771 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -66,7 +66,8 @@ extern int git_buf_try_grow(
  * library, when providing git_buf's, may wish to provide a NULL ptr for
  * ease of handling.  The buffer routines, however, expect a non-NULL ptr
  * always.  This helper method simply handles NULL input, converting to a
- * git_buf__initbuf.
+ * git_buf__initbuf. If a buffer with a non-NULL ptr is passed in, this method
+ * assures that the buffer is '\0'-terminated.
  */
 extern void git_buf_sanitize(git_buf *buf);
 
diff --git a/src/commit.c b/src/commit.c
index 87ab2ab60..05b70a983 100644
--- a/src/commit.c
+++ b/src/commit.c
@@ -642,7 +642,7 @@ int git_commit_header_field(git_buf *out, const git_commit *commit, const char *
 {
 	const char *eol, *buf = commit->raw_header;
 
-	git_buf_sanitize(out);
+	git_buf_clear(out);
 
 	while ((eol = strchr(buf, '\n'))) {
 		/* We can skip continuations here */
@@ -706,8 +706,8 @@ int git_commit_extract_signature(git_buf *signature, git_buf *signed_data, git_r
 	const char *h, *eol;
 	int error;
 
-	git_buf_sanitize(signature);
-	git_buf_sanitize(signed_data);
+	git_buf_clear(signature);
+	git_buf_clear(signed_data);
 
 	if (!field)
 		field = "gpgsig";
@@ -766,8 +766,9 @@ int git_commit_extract_signature(git_buf *signature, git_buf *signed_data, git_r
 		if (git_buf_oom(signature))
 			goto oom;
 
+		error = git_buf_puts(signed_data, eol+1);
 		git_odb_object_free(obj);
-		return git_buf_puts(signed_data, eol+1);
+		return error;
 	}
 
 	giterr_set(GITERR_OBJECT, "this commit is not signed");