diff --git a/include/mbedtls/ecp.h b/include/mbedtls/ecp.h
index 569c581..a69ba17 100644
--- a/include/mbedtls/ecp.h
+++ b/include/mbedtls/ecp.h
@@ -412,7 +412,7 @@
  *
  * \note            buf is updated to point right after the ECPoint on exit
  *
- * \return          O if successful,
+ * \return          0 if successful,
  *                  MBEDTLS_ERR_MPI_XXX if initialization failed
  *                  MBEDTLS_ERR_ECP_BAD_INPUT_DATA if input is invalid
  */
@@ -443,7 +443,7 @@
  * \param grp       Destination group
  * \param index     Index in the list of well-known domain parameters
  *
- * \return          O if successful,
+ * \return          0 if successful,
  *                  MBEDTLS_ERR_MPI_XXX if initialization failed
  *                  MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE for unkownn groups
  *
@@ -461,7 +461,7 @@
  *
  * \note            buf is updated to point right after ECParameters on exit
  *
- * \return          O if successful,
+ * \return          0 if successful,
  *                  MBEDTLS_ERR_MPI_XXX if initialization failed
  *                  MBEDTLS_ERR_ECP_BAD_INPUT_DATA if input is invalid
  */