diff --git a/ChangeLog b/ChangeLog
index 395f4e50c9..eda37a2b31 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2018-03-11  Zack Weinberg  <zackw@panix.com>
+
+	* sysdeps/ieee754/ldbl-opt/nldbl-compat.c: Include math.h
+	before nldbl-compat.h.
+
 2018-03-10  Zack Weinberg  <zackw@panix.com>
 
 	* sysdeps/ieee754/ldbl-opt/math_ldbl_opt.h: Don't include
diff --git a/sysdeps/ieee754/ldbl-opt/nldbl-compat.c b/sysdeps/ieee754/ldbl-opt/nldbl-compat.c
index bf54090d4f..ffb5fabebe 100644
--- a/sysdeps/ieee754/ldbl-opt/nldbl-compat.c
+++ b/sysdeps/ieee754/ldbl-opt/nldbl-compat.c
@@ -20,6 +20,7 @@
 #include <stdarg.h>
 #include <stdio.h>
 #include <libioP.h>
+#include <math.h>
 #include <wchar.h>
 #include <printf.h>
 #include <monetary.h>