diff --git a/include/mbedtls/oid.h b/include/mbedtls/oid.h
index 1284aa9..49f4af5 100644
--- a/include/mbedtls/oid.h
+++ b/include/mbedtls/oid.h
@@ -470,15 +470,20 @@
  * \brief           Translate a string containing a numeric representation
  *                  of an ASN.1 OID into its encoded form
  *                  (e.g. "1.2.840.113549" into "\x2A\x86\x48\x86\xF7\x0D")
+ *                  On success, this function allocates oid->buf from the
+ *                  heap. It must be free'd by the caller.
  *
- * \param buf       buffer to put representation in
- * \param size      size of the buffer
- * \param oid       OID to translate
+ * \param oid       mbedtls_asn1_buf to populate with the DER-encoded OID
+ * \param oid_str   string representation of the OID to parse
+ * \param size      length of the OID string
  *
- * \return          Length of the string written (excluding final NULL) or
- *                  MBEDTLS_ERR_OID_BUF_TOO_SMALL in case of error
+ * \return          0 if successful
+ * \return          #MBEDTLS_ERR_ASN1_INVALID_DATA if oid_str does not
+ *                  represent a valid OID
+ * \return          #MBEDTLS_ERR_ASN1_ALLOC_FAILED if the function fails to
+ *                  allocate oid->buf
  */
-int mbedtls_oid_from_numeric_string(mbedtls_asn1_buf *oid, const char *buf, size_t size);
+int mbedtls_oid_from_numeric_string(mbedtls_asn1_buf *oid, const char *oid_str, size_t size);
 
 /**
  * \brief          Translate an X.509 extension OID into local values
diff --git a/library/oid.c b/library/oid.c
index 06127c2..6c62b94 100644
--- a/library/oid.c
+++ b/library/oid.c
@@ -948,12 +948,12 @@
 
 /* Return the OID for the given x.y.z.... style numeric string  */
 int mbedtls_oid_from_numeric_string(mbedtls_asn1_buf *oid,
-                                    const char *buf, size_t size)
+                                    const char *oid_str, size_t size)
 {
     int ret = MBEDTLS_ERR_ASN1_INVALID_DATA;
 
-    const char *str_ptr = buf;
-    const char *str_bound = buf + size;
+    const char *str_ptr = oid_str;
+    const char *str_bound = oid_str + size;
     int val = 0;
     size_t encoded_len;
 
@@ -1020,7 +1020,7 @@
     oid->len = encoded_len;
 
     /* Now that we've allocated the buffer, go back to the start and encode */
-    str_ptr = buf;
+    str_ptr = oid_str;
     unsigned char *out_ptr = oid->p;
     unsigned char *out_bound = oid->p + oid->len;