diff --git a/cpp2rust/compat/arpa/inet.h b/cpp2rust/compat/arpa/inet.h
index e1d7fc107d..a09ef1a745 100644
--- a/cpp2rust/compat/arpa/inet.h
+++ b/cpp2rust/compat/arpa/inet.h
@@ -8,10 +8,16 @@
 #undef htonl
 #undef htons
 
+#ifdef __cplusplus
+extern "C" {
+#endif
 uint32_t cpp2rust_ntohl(uint32_t x);
 uint16_t cpp2rust_ntohs(uint16_t x);
 uint32_t cpp2rust_htonl(uint32_t x);
 uint16_t cpp2rust_htons(uint16_t x);
+#ifdef __cplusplus
+}
+#endif
 
 #define ntohl(x) cpp2rust_ntohl(x)
 #define ntohs(x) cpp2rust_ntohs(x)
diff --git a/cpp2rust/compat/errno.h b/cpp2rust/compat/errno.h
index d6b34c3040..f0f774a688 100644
--- a/cpp2rust/compat/errno.h
+++ b/cpp2rust/compat/errno.h
@@ -5,6 +5,12 @@
 
 #undef errno
 
+#ifdef __cplusplus
+extern "C" {
+#endif
 int *cpp2rust_errno(void);
+#ifdef __cplusplus
+}
+#endif
 
 #define errno (*cpp2rust_errno())
diff --git a/cpp2rust/compat/sys/select.h b/cpp2rust/compat/sys/select.h
index 2a15d77cd6..d651f8c31e 100644
--- a/cpp2rust/compat/sys/select.h
+++ b/cpp2rust/compat/sys/select.h
@@ -8,10 +8,16 @@
 #undef FD_ISSET
 #undef FD_ZERO
 
+#ifdef __cplusplus
+extern "C" {
+#endif
 void cpp2rust_fd_set(int fd, fd_set *set);
 void cpp2rust_fd_clr(int fd, fd_set *set);
 int cpp2rust_fd_isset(int fd, const fd_set *set);
 void cpp2rust_fd_zero(fd_set *set);
+#ifdef __cplusplus
+}
+#endif
 
 #define FD_SET(fd, set) cpp2rust_fd_set(fd, set)
 #define FD_CLR(fd, set) cpp2rust_fd_clr(fd, set)
diff --git a/tests/unit/out/refcount/size_t_ssize_t.rs b/tests/unit/out/refcount/size_t_ssize_t.rs
index 2ffa46a344..879e340278 100644
--- a/tests/unit/out/refcount/size_t_ssize_t.rs
+++ b/tests/unit/out/refcount/size_t_ssize_t.rs
@@ -208,6 +208,19 @@ fn main_0() -> i32 {
         ((sizes.as_pointer() as Ptr<usize>).to_end()).reinterpret_cast::<usize>();
     assert!((((sizes_end).clone() - (sizes.as_pointer() as Ptr::<usize>)) as i64 == 4_i64));
     assert!((((sizes_end.offset(-((1) as isize))).read()) == 4_usize));
+    let set: Value<CFdSet> = Rc::new(RefCell::new(Default::default()));
+    (set.as_pointer()).with_mut(|__s| __s.zero());
+    (set.as_pointer()).with_mut(|__s| __s.set(3));
+    assert!(
+        (if (set.as_pointer()).with(|__s| __s.isset(3)) {
+            1
+        } else {
+            0
+        } != 0)
+    );
+    libcc2rs::cpp2rust_errno().write(42);
+    assert!(((libcc2rs::cpp2rust_errno().read()) == 42));
+    assert!((u32::from_be(u32::to_be(7_u32)) == 7_u32));
     return 0;
 }
 pub fn __cpp2rust_init_globals() {}
diff --git a/tests/unit/out/unsafe/size_t_ssize_t.rs b/tests/unit/out/unsafe/size_t_ssize_t.rs
index 6ac0235f76..60fbb85cf0 100644
--- a/tests/unit/out/unsafe/size_t_ssize_t.rs
+++ b/tests/unit/out/unsafe/size_t_ssize_t.rs
@@ -197,6 +197,13 @@ unsafe fn main_0() -> i32 {
             == (4_i64))
     );
     assert!(((*(sizes_end.offset(-((1) as isize)))) == (4_usize)));
+    let mut set: ::libc::fd_set = std::mem::zeroed::<::libc::fd_set>();
+    libc::FD_ZERO((&mut set as *mut ::libc::fd_set));
+    libc::FD_SET(3, (&mut set as *mut ::libc::fd_set));
+    assert!((libc::FD_ISSET(3, (&mut set as *mut ::libc::fd_set).cast_const()) as i32 != 0));
+    (*libcc2rs::cpp2rust_errno_unsafe()) = 42;
+    assert!(((*libcc2rs::cpp2rust_errno_unsafe()) == (42)));
+    assert!(((u32::from_be(u32::to_be(7_u32))) == (7_u32)));
     return 0;
 }
 pub unsafe fn __cpp2rust_init_globals() {}
diff --git a/tests/unit/size_t_ssize_t.cpp b/tests/unit/size_t_ssize_t.cpp
index 9c46ed2947..f1606d8af4 100644
--- a/tests/unit/size_t_ssize_t.cpp
+++ b/tests/unit/size_t_ssize_t.cpp
@@ -1,8 +1,11 @@
 #include <algorithm>
+#include <arpa/inet.h>
 #include <cassert>
 #include <cstddef>
 #include <cstdint>
+#include <errno.h>
 #include <iterator>
+#include <sys/select.h>
 #include <sys/types.h>
 #include <utility>
 
@@ -113,5 +116,15 @@ int main() {
   const size_t *sizes_end = std::end(sizes);
   assert(sizes_end - sizes == 4);
   assert(*(sizes_end - 1) == 4);
+
+  fd_set set;
+  FD_ZERO(&set);
+  FD_SET(3, &set);
+  assert(FD_ISSET(3, &set));
+
+  errno = 42;
+  assert(errno == 42);
+
+  assert(ntohl(htonl(7)) == 7);
   return 0;
 }