diff --git a/library/bignum_core.c b/library/bignum_core.c
index 998c06c8fd..ba6c0c13ae 100644
--- a/library/bignum_core.c
+++ b/library/bignum_core.c
@@ -33,16 +33,6 @@
 #include "bn_mul.h"
 #include "constant_time_internal.h"
 
-/**
- * \brief          Count leading zeros
- *
- * \warning        The result is undefined if \p a == 0
- *
- * \param a        The value to operate on
- *
- * \return         The number of leading zeros, if \p a != 0. If \p a == 0, the result
- *                 is undefined.
- */
 inline size_t mbedtls_mpi_core_clz(mbedtls_mpi_uint a)
 {
 #if defined(__has_builtin)
diff --git a/library/bignum_core.h b/library/bignum_core.h
index b3d05a34ef..158d2b3222 100644
--- a/library/bignum_core.h
+++ b/library/bignum_core.h
@@ -101,10 +101,13 @@
     (((X)[(i) / ciL] >> (((i) % ciL) * 8)) & 0xff)
 
 /** Count leading zero bits in a given integer.
+ *
+ * \warning     The result is undefined if \p a == 0
  *
  * \param a     Integer to count leading zero bits.
  *
- * \return      The number of leading zero bits in \p a.
+ * \return      The number of leading zero bits in \p a, if \p a != 0.
+ *              If \p a == 0, the result is undefined.
  */
 size_t mbedtls_mpi_core_clz(mbedtls_mpi_uint a);