diff --git a/sysdeps/ieee754/dbl-64/e_fmod.c b/sysdeps/ieee754/dbl-64/e_fmod.c
index 1b5453609e..9c81f83c80 100644
--- a/sysdeps/ieee754/dbl-64/e_fmod.c
+++ b/sysdeps/ieee754/dbl-64/e_fmod.c
@@ -98,7 +98,7 @@ __fmod (double x, double y)
 
       if (__glibc_unlikely (mx == 0))
 	return asdouble (sx);
-      int shift = clz_uint64 (mx);
+      int shift = stdc_leading_zeros (mx);
       ex -= shift + 1;
       mx <<= shift;
       mx = sx | (mx >> EXPONENT_WIDTH);
@@ -131,10 +131,10 @@ __fmod (double x, double y)
       my = hy;
       ey = 0;
       exp_diff--;
-      lead_zeros_my = clz_uint64 (my);
+      lead_zeros_my = stdc_leading_zeros (my);
     }
 
-  int tail_zeros_my = ctz_uint64 (my);
+  int tail_zeros_my = stdc_trailing_zeros (my);
   int sides_zeroes = lead_zeros_my + tail_zeros_my;
 
   int right_shift = exp_diff < tail_zeros_my ? exp_diff : tail_zeros_my;
diff --git a/sysdeps/ieee754/dbl-64/math_config.h b/sysdeps/ieee754/dbl-64/math_config.h
index d9288c4fb3..99a9e8e7d3 100644
--- a/sysdeps/ieee754/dbl-64/math_config.h
+++ b/sysdeps/ieee754/dbl-64/math_config.h
@@ -23,6 +23,7 @@
 #include <math_private.h>
 #include <nan-high-order-bit.h>
 #include <stdint.h>
+#include <stdbit.h>
 
 #ifndef WANT_ROUNDING
 /* Correct special case results in non-nearest rounding modes.  */
@@ -43,24 +44,6 @@
 # define TOINT_INTRINSICS 0
 #endif
 
-static inline int
-clz_uint64 (uint64_t x)
-{
-  if (sizeof (uint64_t) == sizeof (unsigned long))
-    return __builtin_clzl (x);
-  else
-    return __builtin_clzll (x);
-}
-
-static inline int
-ctz_uint64 (uint64_t x)
-{
-  if (sizeof (uint64_t) == sizeof (unsigned long))
-    return __builtin_ctzl (x);
-  else
-    return __builtin_ctzll (x);
-}
-
 #if TOINT_INTRINSICS
 /* Round x to nearest int in all rounding modes, ties have to be rounded
    consistently with converttoint so the results match.  If the result
@@ -148,7 +131,7 @@ get_exponent (uint64_t x)
 static inline double
 make_double (uint64_t x, int64_t ep, uint64_t s)
 {
-  int lz = clz_uint64 (x) - EXPONENT_WIDTH;
+  int lz = stdc_leading_zeros (x) - EXPONENT_WIDTH;
   x <<= lz;
   ep -= lz;