diff --git a/src/floatfns.c b/src/floatfns.c
index f2b3b13acd8..293184c70f1 100644
--- a/src/floatfns.c
+++ b/src/floatfns.c
@@ -29,14 +29,20 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 
    C99 and C11 require the following math.h functions in addition to
    the C89 functions.  Of these, Emacs currently exports only the
-   starred ones to Lisp, since we haven't found a use for the others:
-   acosh, atanh, cbrt, *copysign, erf, erfc, exp2, expm1, fdim, fma,
-   fmax, fmin, fpclassify, hypot, ilogb, isfinite, isgreater,
-   isgreaterequal, isinf, isless, islessequal, islessgreater, *isnan,
-   isnormal, isunordered, lgamma, log1p, *log2 [via (log X 2)], *logb
-   (approximately), lrint/llrint, lround/llround, nan, nearbyint,
-   nextafter, nexttoward, remainder, remquo, *rint, round, scalbln,
-   scalbn, signbit, tgamma, *trunc.
+   starred ones to Lisp, since we haven't found a use for the others.
+   Also, it uses the ones marked "+" internally:
+   acosh, atanh, cbrt, copysign (implemented by signbit), erf, erfc,
+   exp2, expm1, fdim, fma, fmax, fmin, fpclassify, hypot, +ilogb,
+   isfinite, isgreater, isgreaterequal, isinf, isless, islessequal,
+   islessgreater, *isnan, isnormal, isunordered, lgamma, log1p, *log2
+   [via (log X 2)], logb (approximately; implemented by frexp),
+   +lrint/llrint, +lround/llround, nan, nearbyint, nextafter,
+   nexttoward, remainder, remquo, *rint, round, scalbln, +scalbn,
+   +signbit, tgamma, *trunc.
+
+   The C standard also requires functions for float and long double
+   that are not listed above.  Of these functions, Emacs uses only the
+   following internally: fabsf, powf, sprintf.
  */
 
 #include <config.h>