diff --git a/setup/build.py b/setup/build.py
index d6de2eb1b0..a720370559 100644
--- a/setup/build.py
+++ b/setup/build.py
@@ -34,6 +34,13 @@ class Extension(object):
         self.error = d['error'] = kwargs.get('error', None)
         self.libraries = d['libraries'] = kwargs.get('libraries', [])
         self.cflags = d['cflags'] = kwargs.get('cflags', [])
+        if iswindows:
+            self.cflags.append('/DCALIBRE_MODINIT_FUNC=PyMODINIT_FUNC')
+        else:
+            if self.needs_cxx:
+                self.cflags.append('-DCALIBRE_MODINIT_FUNC=extern "C" __attribute__ ((visibility ("default"))) void')
+            else:
+                self.cflags.append('-DCALIBRE_MODINIT_FUNC=__attribute__ ((visibility ("default"))) void')
         self.ldflags = d['ldflags'] = kwargs.get('ldflags', [])
         self.optional = d['options'] = kwargs.get('optional', False)
         of = kwargs.get('optimize_level', None)
@@ -145,6 +152,7 @@ def init_env():
         ldflags = shlex.split(ldflags)
         cflags += shlex.split(os.environ.get('CFLAGS', ''))
         ldflags += shlex.split(os.environ.get('LDFLAGS', ''))
+        cflags += ['-fvisibility=hidden']
 
     if islinux:
         cflags.append('-pthread')
diff --git a/src/calibre/devices/libusb/libusb.c b/src/calibre/devices/libusb/libusb.c
index 843459cd98..5cef316a5d 100644
--- a/src/calibre/devices/libusb/libusb.c
+++ b/src/calibre/devices/libusb/libusb.c
@@ -119,7 +119,7 @@ static PyMethodDef libusb_methods[] = {
     {NULL, NULL, 0, NULL}
 };
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initlibusb(void) {
     PyObject *m;
 
diff --git a/src/calibre/devices/mtp/unix/libmtp.c b/src/calibre/devices/mtp/unix/libmtp.c
index 9539a4b7d7..086211484c 100644
--- a/src/calibre/devices/mtp/unix/libmtp.c
+++ b/src/calibre/devices/mtp/unix/libmtp.c
@@ -712,7 +712,7 @@ static PyMethodDef libmtp_methods[] = {
 };
 
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initlibmtp(void) {
     PyObject *m;
 
diff --git a/src/calibre/devices/mtp/windows/wpd.cpp b/src/calibre/devices/mtp/windows/wpd.cpp
index 867ce6bcee..6901d5472e 100644
--- a/src/calibre/devices/mtp/windows/wpd.cpp
+++ b/src/calibre/devices/mtp/windows/wpd.cpp
@@ -182,7 +182,7 @@ static PyMethodDef wpd_methods[] = {
 };
 
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initwpd(void) {
     PyObject *m;
 
diff --git a/src/calibre/devices/usbobserver/usbobserver.c b/src/calibre/devices/usbobserver/usbobserver.c
index 3b4f3aa546..c3ac61d718 100644
--- a/src/calibre/devices/usbobserver/usbobserver.c
+++ b/src/calibre/devices/usbobserver/usbobserver.c
@@ -482,7 +482,7 @@ static PyMethodDef usbobserver_methods[] = {
     {NULL, NULL, 0, NULL}
 };
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initusbobserver(void) {
     (void) Py_InitModule("usbobserver", usbobserver_methods);
 }
diff --git a/src/calibre/ebooks/compression/palmdoc.c b/src/calibre/ebooks/compression/palmdoc.c
index ac4a6c9097..7c29372481 100644
--- a/src/calibre/ebooks/compression/palmdoc.c
+++ b/src/calibre/ebooks/compression/palmdoc.c
@@ -195,7 +195,7 @@ static PyMethodDef cPalmdocMethods[] = {
     {NULL, NULL, 0, NULL}
 };
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initcPalmdoc(void) {
     PyObject *m;
     m = Py_InitModule3("cPalmdoc", cPalmdocMethods,
diff --git a/src/calibre/ebooks/djvu/bzzdecoder.c b/src/calibre/ebooks/djvu/bzzdecoder.c
index 0df9e488ff..1e355609f9 100644
--- a/src/calibre/ebooks/djvu/bzzdecoder.c
+++ b/src/calibre/ebooks/djvu/bzzdecoder.c
@@ -694,7 +694,7 @@ static PyMethodDef bzzdecmethods[] = {
 
 
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initbzzdec(void) {
     PyObject *m;
     m = Py_InitModule3("bzzdec", bzzdecmethods,
diff --git a/src/calibre/gui2/tweak_book/diff/_patiencediff_c.c b/src/calibre/gui2/tweak_book/diff/_patiencediff_c.c
index 0f0d380716..6af903376a 100644
--- a/src/calibre/gui2/tweak_book/diff/_patiencediff_c.c
+++ b/src/calibre/gui2/tweak_book/diff/_patiencediff_c.c
@@ -1258,7 +1258,7 @@ static PyMethodDef cpatiencediff_methods[] = {
 };
 
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 init_patiencediff_c(void)
 {
     PyObject* m;
diff --git a/src/calibre/gui2/tweak_book/editor/syntax/html.c b/src/calibre/gui2/tweak_book/editor/syntax/html.c
index 21ce39e69e..7b0fed55f4 100644
--- a/src/calibre/gui2/tweak_book/editor/syntax/html.c
+++ b/src/calibre/gui2/tweak_book/editor/syntax/html.c
@@ -474,7 +474,7 @@ static PyMethodDef html_methods[] = {
 };
 
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 inithtml(void) {
     PyObject *m, *temp;
     if (PyType_Ready(&html_TagType) < 0)
diff --git a/src/calibre/library/sqlite_custom.c b/src/calibre/library/sqlite_custom.c
index 8b45044ca9..c24c58f15a 100644
--- a/src/calibre/library/sqlite_custom.c
+++ b/src/calibre/library/sqlite_custom.c
@@ -10,7 +10,7 @@ SQLITE_EXTENSION_INIT1
 #ifdef _MSC_VER
 #define MYEXPORT __declspec(dllexport)
 #else
-#define MYEXPORT
+#define MYEXPORT __attribute__ ((visibility ("default")))
 #endif
 
 // sortconcat {{{
@@ -271,7 +271,7 @@ static PyMethodDef sqlite_custom_methods[] = {
     {NULL, NULL, 0, NULL}
 };
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initsqlite_custom(void) {
     PyObject *m;
     m = Py_InitModule3("sqlite_custom", sqlite_custom_methods,
diff --git a/src/calibre/utils/certgen.c b/src/calibre/utils/certgen.c
index 730e8da709..2770156c38 100644
--- a/src/calibre/utils/certgen.c
+++ b/src/calibre/utils/certgen.c
@@ -379,7 +379,7 @@ static PyMethodDef certgen_methods[] = {
 };
 
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initcertgen(void) {
     PyObject *m;
     m = Py_InitModule3("certgen", certgen_methods,
diff --git a/src/calibre/utils/chm/extra.c b/src/calibre/utils/chm/extra.c
index bafbf7bb07..b4fc13488a 100644
--- a/src/calibre/utils/chm/extra.c
+++ b/src/calibre/utils/chm/extra.c
@@ -708,7 +708,7 @@ IndexMethods[] = {
 #ifdef __cplusplus
 extern "C"
 #endif
-MODEXPORT(void)
+CALIBRE_MODINIT_FUNC
 initchm_extra (void) {
   Py_InitModule ("chm_extra", IndexMethods);
 }
diff --git a/src/calibre/utils/chm/swig_chm.c b/src/calibre/utils/chm/swig_chm.c
index 56017205b7..7a1e1dc776 100644
--- a/src/calibre/utils/chm/swig_chm.c
+++ b/src/calibre/utils/chm/swig_chm.c
@@ -1106,7 +1106,7 @@ static swig_const_info swig_const_table[] = {
 #ifdef __cplusplus
 extern "C"
 #endif
-SWIGEXPORT(void) SWIG_init(void) {
+CALIBRE_MODINIT_FUNC SWIG_init(void) {
     static PyObject *SWIG_globals = 0; 
     static int       typeinit = 0;
     PyObject *m, *d;
diff --git a/src/calibre/utils/fonts/freetype.cpp b/src/calibre/utils/fonts/freetype.cpp
index 58d014c6b9..f9242f1fcf 100644
--- a/src/calibre/utils/fonts/freetype.cpp
+++ b/src/calibre/utils/fonts/freetype.cpp
@@ -293,7 +293,7 @@ PyMethodDef methods[] = {
     {NULL, NULL, 0, NULL}
 };
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initfreetype(void) {
     PyObject *m;
 
diff --git a/src/calibre/utils/fonts/winfonts.cpp b/src/calibre/utils/fonts/winfonts.cpp
index db023b14bb..9e15bda6e6 100644
--- a/src/calibre/utils/fonts/winfonts.cpp
+++ b/src/calibre/utils/fonts/winfonts.cpp
@@ -235,7 +235,7 @@ PyMethodDef winfonts_methods[] = {
 };
 
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initwinfonts(void) {
     PyObject *m;
     m = Py_InitModule3(
diff --git a/src/calibre/utils/icu.c b/src/calibre/utils/icu.c
index 9b3699f196..3c52cb3265 100644
--- a/src/calibre/utils/icu.c
+++ b/src/calibre/utils/icu.c
@@ -1175,7 +1175,7 @@ static PyMethodDef icu_methods[] = {
 
 #define ADDUCONST(x) PyModule_AddIntConstant(m, #x, x)
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initicu(void) 
 {
     PyObject* m;
diff --git a/src/calibre/utils/lzx/lzxmodule.c b/src/calibre/utils/lzx/lzxmodule.c
index 8b4b1f7c9b..410ade709d 100644
--- a/src/calibre/utils/lzx/lzxmodule.c
+++ b/src/calibre/utils/lzx/lzxmodule.c
@@ -202,7 +202,7 @@ static PyMethodDef lzx_methods[] = {
     { NULL }
 };
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initlzx(void)
 {
     PyObject *m;
diff --git a/src/calibre/utils/matcher.c b/src/calibre/utils/matcher.c
index a06f468cf5..94ddd9ac35 100644
--- a/src/calibre/utils/matcher.c
+++ b/src/calibre/utils/matcher.c
@@ -508,7 +508,7 @@ static PyMethodDef matcher_methods[] = {
 };
 
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initmatcher(void) {
     PyObject *m;
     MatcherType.tp_new = PyType_GenericNew;
diff --git a/src/calibre/utils/monotonic.c b/src/calibre/utils/monotonic.c
index 00fb1dbc73..beb8f91f8d 100644
--- a/src/calibre/utils/monotonic.c
+++ b/src/calibre/utils/monotonic.c
@@ -71,7 +71,7 @@ static PyMethodDef monotonic_methods[] = {
     {NULL, NULL, 0, NULL}
 };
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initmonotonic(void) {
     PyObject *m;
 #ifdef _MSC_VER
diff --git a/src/calibre/utils/msdes/msdesmodule.c b/src/calibre/utils/msdes/msdesmodule.c
index 27ca46ffcb..66844fa510 100644
--- a/src/calibre/utils/msdes/msdesmodule.c
+++ b/src/calibre/utils/msdes/msdesmodule.c
@@ -78,7 +78,7 @@ static PyMethodDef msdes_methods[] = {
     { NULL, NULL }
 };
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initmsdes(void)
 {
     PyObject *m;
diff --git a/src/calibre/utils/podofo/podofo.cpp b/src/calibre/utils/podofo/podofo.cpp
index 250c18b4a8..d4c6b58e91 100644
--- a/src/calibre/utils/podofo/podofo.cpp
+++ b/src/calibre/utils/podofo/podofo.cpp
@@ -38,7 +38,7 @@ class PyLogMessage : public PdfError::LogMessageCallback {
 
 PyLogMessage log_message;
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initpodofo(void) 
 {
     PyObject* m;
diff --git a/src/calibre/utils/speedup.c b/src/calibre/utils/speedup.c
index 93d13c020e..0c489bc919 100644
--- a/src/calibre/utils/speedup.c
+++ b/src/calibre/utils/speedup.c
@@ -483,7 +483,7 @@ static PyMethodDef speedup_methods[] = {
 };
 
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initspeedup(void) {
     PyObject *m;
     m = Py_InitModule3("speedup", speedup_methods,
diff --git a/src/calibre/utils/spell/hunspell_wrapper.cpp b/src/calibre/utils/spell/hunspell_wrapper.cpp
index bdd61842af..09b3bdaf65 100644
--- a/src/calibre/utils/spell/hunspell_wrapper.cpp
+++ b/src/calibre/utils/spell/hunspell_wrapper.cpp
@@ -165,7 +165,7 @@ static PyTypeObject DictionaryType = {
 };
 
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 inithunspell(void) {
     PyObject *mod;
 
@@ -185,4 +185,3 @@ inithunspell(void) {
     Py_INCREF(&DictionaryType);
     PyModule_AddObject(mod, "Dictionary", (PyObject *)&DictionaryType);
 }
-
diff --git a/src/calibre/utils/unrar.cpp b/src/calibre/utils/unrar.cpp
index 20dc0f72f8..625642a776 100644
--- a/src/calibre/utils/unrar.cpp
+++ b/src/calibre/utils/unrar.cpp
@@ -526,7 +526,7 @@ static PyTypeObject RARArchiveType = { // {{{
 // }}} End RARArchive
 
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initunrar(void) {
     PyObject *m;
 
diff --git a/src/calibre/utils/windows/winutil.c b/src/calibre/utils/windows/winutil.c
index d4caa0be44..dee10862f0 100644
--- a/src/calibre/utils/windows/winutil.c
+++ b/src/calibre/utils/windows/winutil.c
@@ -384,7 +384,7 @@ be a unicode string. Returns unicode strings."
     {NULL, NULL, 0, NULL}
 };
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initwinutil(void) {
     PyObject *m;
     m = Py_InitModule3("winutil", WinutilMethods,
diff --git a/src/calibre/utils/zlib2.c b/src/calibre/utils/zlib2.c
index 601687a07f..aa6f4682a6 100644
--- a/src/calibre/utils/zlib2.c
+++ b/src/calibre/utils/zlib2.c
@@ -383,7 +383,7 @@ static PyMethodDef methods[] = {
     {NULL, NULL, 0, NULL}
 };
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initzlib2(void) {
     PyObject *m, *ver;
     Comptype.tp_new = PyType_GenericNew;
diff --git a/src/duktape/module.c b/src/duktape/module.c
index 864be7f06d..79a93c1748 100644
--- a/src/duktape/module.c
+++ b/src/duktape/module.c
@@ -63,7 +63,12 @@ static struct PyModuleDef moduledef = {
 };
 #endif
 
-PyMODINIT_FUNC
+#ifdef _MSVC
+#define EXPORTED __declspec(dllexport)
+#else
+#define EXPORTED __attribute__ ((visibility ("default")))
+#endif
+EXPORTED PyMODINIT_FUNC
 #if PY_MAJOR_VERSION >= 3
 PyInit_dukpy(void)
 #else 
diff --git a/src/lzma/lzma_binding.c b/src/lzma/lzma_binding.c
index b6f787fe53..c01fdd0e77 100644
--- a/src/lzma/lzma_binding.c
+++ b/src/lzma/lzma_binding.c
@@ -412,7 +412,7 @@ static PyMethodDef lzma_binding_methods[] = {
 };
 
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 initlzma_binding(void) {
     PyObject *m = NULL, *preset_map = NULL, *temp = NULL;
     int i = 0;
diff --git a/src/tinycss/tokenizer.c b/src/tinycss/tokenizer.c
index 19238ca4a6..98e7f0d6ec 100644
--- a/src/tinycss/tokenizer.c
+++ b/src/tinycss/tokenizer.c
@@ -416,7 +416,7 @@ static PyMethodDef tokenizer_methods[] = {
 };
 
 
-PyMODINIT_FUNC
+CALIBRE_MODINIT_FUNC
 inittokenizer(void) {
     PyObject *m;
     if (PyType_Ready(&tokenizer_TokenType) < 0)