diff --git a/Source/cmStandardLexer.h b/Source/cmStandardLexer.h
index fe69a86ee8..71e40d8ccf 100644
--- a/Source/cmStandardLexer.h
+++ b/Source/cmStandardLexer.h
@@ -23,6 +23,12 @@
 // NOLINTNEXTLINE(bugprone-reserved-identifier)
 #  define _XOPEN_SOURCE 700
 #endif
+#if defined(__APPLE__)
+// Restore Darwin APIs removed by _POSIX_C_SOURCE:
+//   aligned_alloc
+// NOLINTNEXTLINE(bugprone-reserved-identifier)
+#  define _DARWIN_C_SOURCE
+#endif
 
 #include "cmsys/Configure.h" // IWYU pragma: keep
 
diff --git a/Source/cmTimestamp.cxx b/Source/cmTimestamp.cxx
index fdeff04a51..82fab531ca 100644
--- a/Source/cmTimestamp.cxx
+++ b/Source/cmTimestamp.cxx
@@ -11,6 +11,13 @@
 // NOLINTNEXTLINE(bugprone-reserved-identifier)
 #  define _XOPEN_SOURCE 700
 #endif
+#if defined(__APPLE__)
+// Restore Darwin APIs removed by _POSIX_C_SOURCE:
+//   aligned_alloc
+//   timespec_get
+// NOLINTNEXTLINE(bugprone-reserved-identifier)
+#  define _DARWIN_C_SOURCE
+#endif
 
 #include "cmTimestamp.h"