diff --git a/NEWS.md b/NEWS.md
index c76736e50..3f2fd8df5 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -32,6 +32,8 @@
 
 6. `rowwiseDT()` now provides a helpful error message when a complex object that is not a list (e.g., a function) is provided as a cell value, instructing the user to wrap it in `list()`, [#7219](https://github.com/Rdatatable/data.table/issues/7219). Thanks @kylebutts for the report and @venom1204 for the fix.
 
+7. Fixed compilation failure like "error: unknown type name 'siginfo_t'" in v1.18.0 in some strict environments, e.g., FreeBSD, where the header file declaring the POSIX function `waitid` does not transitively include the header file defining the `siginfo_t` type, [#7516](https://github.com/rdatatable/data.table/issues/7516). Thanks to @jszhao for the report and @aitap for the fix.
+
 ### Notes
 
 1. {data.table} now depends on R 3.5.0 (2018).
diff --git a/src/utils.c b/src/utils.c
index 50fefeb66..5f5da238f 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -1,6 +1,10 @@
 #ifndef _WIN32
-#  define _POSIX_C_SOURCE 200809L // required for POSIX (not standard C) features in is_direct_child e.g. 'siginfo_t'
-#  include <sys/wait.h>
+#  if !defined(_POSIX_C_SOURCE) || _POSIX_C_SOURCE < 200809L
+#    undef _POSIX_C_SOURCE
+#    define _POSIX_C_SOURCE 200809L // required for POSIX (not standard C) features in is_direct_child e.g. 'siginfo_t'
+#  endif
+#  include <signal.h> // siginfo_t
+#  include <sys/wait.h> // waitid
 #endif
 
 #include "data.table.h"