diff --git a/Changes b/Changes
index 1ec5ffe71..688b8080f 100644
--- a/Changes
+++ b/Changes
@@ -485,6 +485,9 @@ Working version
   it with -link.
   (David Allsopp, review by Xavier Leroy)
 
+- #9927: Restore Cygwin64 support.
+  (David Allsopp, review by Xavier Leroy)
+
 
 OCaml 4.11.1
 ------------
diff --git a/bytecomp/bytelink.ml b/bytecomp/bytelink.ml
index 6660fee46..fd5bd490a 100644
--- a/bytecomp/bytelink.ml
+++ b/bytecomp/bytelink.ml
@@ -466,7 +466,8 @@ let link_bytecode_as_c tolink outfile with_main =
     (fun () ->
        (* The bytecode *)
        output_string outchan "\
-#define CAML_INTERNALS\
+#define CAML_INTERNALS\n\
+#define CAMLDLLIMPORT\
 \n\
 \n#ifdef __cplusplus\
 \nextern \"C\" {\
diff --git a/otherlibs/systhreads/st_stubs.c b/otherlibs/systhreads/st_stubs.c
index 9c96df54f..d27e14230 100644
--- a/otherlibs/systhreads/st_stubs.c
+++ b/otherlibs/systhreads/st_stubs.c
@@ -35,7 +35,9 @@
 #endif
 #include "caml/sys.h"
 #include "caml/memprof.h"
-#include "threads.h"
+
+/* threads.h is *not* included since it contains the _external_ declarations for
+   the caml_c_thread_register and caml_c_thread_unregister functions. */
 
 #if defined(NATIVE_CODE) && defined(WITH_SPACETIME)
 #include "caml/spacetime.h"
diff --git a/runtime/Makefile b/runtime/Makefile
index 9cccfd069..f688af70a 100644
--- a/runtime/Makefile
+++ b/runtime/Makefile
@@ -130,6 +130,8 @@ ifneq "$(CCOMPTYPE)" "msvc"
 OC_CFLAGS += -g
 endif
 
+OC_CPPFLAGS += -DCAMLDLLIMPORT=
+
 OC_NATIVE_CPPFLAGS = -DNATIVE_CODE -DTARGET_$(ARCH)
 
 ifeq "$(UNIX_OR_WIN32)" "unix"
diff --git a/runtime/caml/misc.h b/runtime/caml/misc.h
index f1029ed06..5c3631033 100644
--- a/runtime/caml/misc.h
+++ b/runtime/caml/misc.h
@@ -74,13 +74,20 @@ CAMLdeprecated_typedef(addr, char *);
   #define Noreturn
 #endif
 
-
-
 /* Export control (to mark primitives and to handle Windows DLL) */
 
+#ifndef CAMLDLLIMPORT
+  #if defined(SUPPORT_DYNAMIC_LINKING) && defined(ARCH_SIXTYFOUR) \
+      && defined(__CYGWIN__)
+    #define CAMLDLLIMPORT __declspec(dllimport)
+  #else
+    #define CAMLDLLIMPORT
+  #endif
+#endif
+
 #define CAMLexport
 #define CAMLprim
-#define CAMLextern extern
+#define CAMLextern CAMLDLLIMPORT extern
 
 /* Weak function definitions that can be overridden by external libs */
 /* Conservatively restricted to ELF and MacOSX platforms */
diff --git a/testsuite/tests/lib-dynlink-bytecode/stub2.c b/testsuite/tests/lib-dynlink-bytecode/stub2.c
index f4cd3a7ee..403bcd555 100644
--- a/testsuite/tests/lib-dynlink-bytecode/stub2.c
+++ b/testsuite/tests/lib-dynlink-bytecode/stub2.c
@@ -18,7 +18,7 @@
 #include "caml/alloc.h"
 #include <stdio.h>
 
-extern value stub1(void);
+CAMLextern value stub1(void);
 
 value stub2(void) {
   printf("This is stub2, calling stub1:\n"); fflush(stdout);