diff --git a/CMakeLists.txt b/CMakeLists.txt
index b952d7bf..d555d25a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -134,7 +134,12 @@ check_c_source_compiles("
     f(void) {}
     int main(void) { return 0; }
 " HAVE_FUNC_ATTRIBUTE_DESTRUCTOR)
-check_symbol_exists(getentropy "sys/random.h" HAVE_DECL_GETENTROPY)
+if (APPLE)
+    # In old macOS SDKs (ex: 10.15), sys/random.h fails to include header files it needs, so add them here.
+    check_symbol_exists(getentropy "Availability.h;stddef.h;sys/random.h" HAVE_GETENTROPY)
+else()
+    check_symbol_exists(getentropy sys/random.h HAVE_GETENTROPY)
+endif()
 check_symbol_exists(glob "glob.h" HAVE_DECL_GLOB)
 check_symbol_exists(mmap "sys/mman.h" HAVE_DECL_MMAP)
 check_include_files(stdint.h HAVE_STDINT_H)