diff --git a/CMakeLists.txt b/CMakeLists.txt
index fa71db9..ca06e68 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -123,6 +123,7 @@ amduat_link(tgk amduat_asl amduat_enc amduat_hash_asl1 amduat_util)
 
 amduat_add_lib(asl_store_fs SRCS ${AMDUAT_ASL_STORE_FS_SRCS})
 amduat_link(asl_store_fs amduat_asl amduat_enc amduat_hash_asl1 amduat_util)
+target_compile_definitions(amduat_asl_store_fs_obj PRIVATE _POSIX_C_SOURCE=200809L)
 
 amduat_add_lib(tgk_store_mem SRCS ${AMDUAT_TGK_STORE_MEM_SRCS})
 amduat_link(tgk_store_mem amduat_tgk amduat_asl amduat_enc amduat_hash_asl1 amduat_util)