diff --git a/include/private/buf.h b/include/private/buf.h
index bff213df..c18eed42 100644
--- a/include/private/buf.h
+++ b/include/private/buf.h
@@ -3,45 +3,68 @@
 
 #include <libxml/tree.h>
 
-xmlBufPtr xmlBufCreate(void);
-xmlBufPtr xmlBufCreateSize(size_t size);
+XML_HIDDEN xmlBufPtr
+xmlBufCreate(void);
+XML_HIDDEN xmlBufPtr
+xmlBufCreateSize(size_t size);
 
-int xmlBufSetAllocationScheme(xmlBufPtr buf,
-                              xmlBufferAllocationScheme scheme);
-int xmlBufGetAllocationScheme(xmlBufPtr buf);
+XML_HIDDEN int
+xmlBufSetAllocationScheme(xmlBufPtr buf, xmlBufferAllocationScheme scheme);
+XML_HIDDEN int
+xmlBufGetAllocationScheme(xmlBufPtr buf);
 
-void xmlBufFree(xmlBufPtr buf);
-void xmlBufEmpty(xmlBufPtr buf);
+XML_HIDDEN void
+xmlBufFree(xmlBufPtr buf);
+XML_HIDDEN void
+xmlBufEmpty(xmlBufPtr buf);
 
 /* size_t xmlBufShrink(xmlBufPtr buf, size_t len); */
-int xmlBufGrow(xmlBufPtr buf, int len);
-int xmlBufResize(xmlBufPtr buf, size_t len);
+XML_HIDDEN int
+xmlBufGrow(xmlBufPtr buf, int len);
+XML_HIDDEN int
+xmlBufResize(xmlBufPtr buf, size_t len);
 
-int xmlBufAdd(xmlBufPtr buf, const xmlChar *str, int len);
-int xmlBufCat(xmlBufPtr buf, const xmlChar *str);
-int xmlBufCCat(xmlBufPtr buf, const char *str);
-int xmlBufWriteQuotedString(xmlBufPtr buf, const xmlChar *string);
+XML_HIDDEN int
+xmlBufAdd(xmlBufPtr buf, const xmlChar *str, int len);
+XML_HIDDEN int
+xmlBufCat(xmlBufPtr buf, const xmlChar *str);
+XML_HIDDEN int
+xmlBufCCat(xmlBufPtr buf, const char *str);
+XML_HIDDEN int
+xmlBufWriteQuotedString(xmlBufPtr buf, const xmlChar *string);
 
-size_t xmlBufAvail(const xmlBufPtr buf);
-size_t xmlBufLength(const xmlBufPtr buf);
+XML_HIDDEN size_t
+xmlBufAvail(const xmlBufPtr buf);
+XML_HIDDEN size_t
+xmlBufLength(const xmlBufPtr buf);
 /* size_t xmlBufUse(const xmlBufPtr buf); */
-int xmlBufIsEmpty(const xmlBufPtr buf);
-int xmlBufAddLen(xmlBufPtr buf, size_t len);
+XML_HIDDEN int
+xmlBufIsEmpty(const xmlBufPtr buf);
+XML_HIDDEN int
+xmlBufAddLen(xmlBufPtr buf, size_t len);
 
 /* const xmlChar * xmlBufContent(const xmlBuf *buf); */
 /* const xmlChar * xmlBufEnd(xmlBufPtr buf); */
 
-xmlChar * xmlBufDetach(xmlBufPtr buf);
+XML_HIDDEN xmlChar *
+xmlBufDetach(xmlBufPtr buf);
 
-size_t xmlBufDump(FILE *file, xmlBufPtr buf);
+XML_HIDDEN size_t
+xmlBufDump(FILE *file, xmlBufPtr buf);
 
-xmlBufPtr xmlBufFromBuffer(xmlBufferPtr buffer);
-xmlBufferPtr xmlBufBackToBuffer(xmlBufPtr buf);
-int xmlBufMergeBuffer(xmlBufPtr buf, xmlBufferPtr buffer);
+XML_HIDDEN xmlBufPtr
+xmlBufFromBuffer(xmlBufferPtr buffer);
+XML_HIDDEN xmlBufferPtr
+xmlBufBackToBuffer(xmlBufPtr buf);
+XML_HIDDEN int
+xmlBufMergeBuffer(xmlBufPtr buf, xmlBufferPtr buffer);
 
-int xmlBufResetInput(xmlBufPtr buf, xmlParserInputPtr input);
-size_t xmlBufGetInputBase(xmlBufPtr buf, xmlParserInputPtr input);
-int xmlBufSetInputBaseCur(xmlBufPtr buf, xmlParserInputPtr input,
-                          size_t base, size_t cur);
+XML_HIDDEN int
+xmlBufResetInput(xmlBufPtr buf, xmlParserInputPtr input);
+XML_HIDDEN size_t
+xmlBufGetInputBase(xmlBufPtr buf, xmlParserInputPtr input);
+XML_HIDDEN int
+xmlBufSetInputBaseCur(xmlBufPtr buf, xmlParserInputPtr input,
+                      size_t base, size_t cur);
 
 #endif /* XML_BUF_H_PRIVATE__ */
diff --git a/include/private/dict.h b/include/private/dict.h
index 42bebffb..fcc10bac 100644
--- a/include/private/dict.h
+++ b/include/private/dict.h
@@ -1,8 +1,11 @@
 #ifndef XML_DICT_H_PRIVATE__
 #define XML_DICT_H_PRIVATE__
 
-int __xmlInitializeDict(void);
-void xmlCleanupDictInternal(void);
-int __xmlRandom(void);
+XML_HIDDEN int
+__xmlInitializeDict(void);
+XML_HIDDEN void
+xmlCleanupDictInternal(void);
+XML_HIDDEN int
+__xmlRandom(void);
 
 #endif /* XML_DICT_H_PRIVATE__ */
diff --git a/include/private/enc.h b/include/private/enc.h
index 77a5b98d..ddfc8aea 100644
--- a/include/private/enc.h
+++ b/include/private/enc.h
@@ -4,10 +4,14 @@
 #include <libxml/encoding.h>
 #include <libxml/tree.h>
 
-void xmlInitEncodingInternal(void);
+XML_HIDDEN void
+xmlInitEncodingInternal(void);
 
-int xmlCharEncFirstLineInput(xmlParserInputBufferPtr input, int len);
-int xmlCharEncInput(xmlParserInputBufferPtr input, int flush);
-int xmlCharEncOutput(xmlOutputBufferPtr output, int init);
+XML_HIDDEN int
+xmlCharEncFirstLineInput(xmlParserInputBufferPtr input, int len);
+XML_HIDDEN int
+xmlCharEncInput(xmlParserInputBufferPtr input, int flush);
+XML_HIDDEN int
+xmlCharEncOutput(xmlOutputBufferPtr output, int init);
 
 #endif /* XML_ENC_H_PRIVATE__ */
diff --git a/include/private/entities.h b/include/private/entities.h
index 9be17bb3..1118c6d0 100644
--- a/include/private/entities.h
+++ b/include/private/entities.h
@@ -4,6 +4,7 @@
 #include <libxml/tree.h>
 #include <libxml/xmlstring.h>
 
-xmlChar *xmlEncodeAttributeEntities(xmlDocPtr doc, const xmlChar *input);
+XML_HIDDEN xmlChar *
+xmlEncodeAttributeEntities(xmlDocPtr doc, const xmlChar *input);
 
 #endif /* XML_ENTITIES_H_PRIVATE__ */
diff --git a/include/private/error.h b/include/private/error.h
index c76e0733..7f284f98 100644
--- a/include/private/error.h
+++ b/include/private/error.h
@@ -4,17 +4,17 @@
 #include <libxml/xmlerror.h>
 #include <libxml/xmlversion.h>
 
-void
+XML_HIDDEN void
 __xmlRaiseError(xmlStructuredErrorFunc schannel,
                 xmlGenericErrorFunc channel, void *data, void *ctx,
                 void *nod, int domain, int code, xmlErrorLevel level,
                 const char *file, int line, const char *str1,
                 const char *str2, const char *str3, int int1, int col,
 	        const char *msg, ...) LIBXML_ATTR_FORMAT(16,17);
-void
+XML_HIDDEN void
 __xmlSimpleError(int domain, int code, xmlNodePtr node,
                  const char *msg, const char *extra) LIBXML_ATTR_FORMAT(4,0);
-void
+XML_HIDDEN void
 xmlGenericErrorDefaultFunc(void *ctx, const char *msg,
                            ...) LIBXML_ATTR_FORMAT(2,3);
 
diff --git a/include/private/globals.h b/include/private/globals.h
index 3ec179b7..5f3f1122 100644
--- a/include/private/globals.h
+++ b/include/private/globals.h
@@ -1,7 +1,9 @@
 #ifndef XML_GLOBALS_H_PRIVATE__
 #define XML_GLOBALS_H_PRIVATE__
 
-void xmlInitGlobalsInternal(void);
-void xmlCleanupGlobalsInternal(void);
+XML_HIDDEN void
+xmlInitGlobalsInternal(void);
+XML_HIDDEN void
+xmlCleanupGlobalsInternal(void);
 
 #endif /* XML_GLOBALS_H_PRIVATE__ */
diff --git a/include/private/html.h b/include/private/html.h
index 8f77d338..6b499296 100644
--- a/include/private/html.h
+++ b/include/private/html.h
@@ -5,7 +5,8 @@
 
 #ifdef LIBXML_HTML_ENABLED
 
-void __htmlParseContent(void *ctx);
+XML_HIDDEN void
+__htmlParseContent(void *ctx);
 
 #endif /* LIBXML_HTML_ENABLED */
 
diff --git a/include/private/io.h b/include/private/io.h
index 9a1e684e..86a72e15 100644
--- a/include/private/io.h
+++ b/include/private/io.h
@@ -5,12 +5,14 @@
 #include <libxml/tree.h>
 #include <libxml/xmlversion.h>
 
-void __xmlIOErr(int domain, int code, const char *extra);
-void __xmlLoaderErr(void *ctx, const char *msg,
-                    const char *filename) LIBXML_ATTR_FORMAT(2,0);
+XML_HIDDEN void
+__xmlIOErr(int domain, int code, const char *extra);
+XML_HIDDEN void
+__xmlLoaderErr(void *ctx, const char *msg,
+               const char *filename) LIBXML_ATTR_FORMAT(2,0);
 
 #ifdef LIBXML_OUTPUT_ENABLED
-xmlOutputBufferPtr
+XML_HIDDEN xmlOutputBufferPtr
 xmlAllocOutputBufferInternal(xmlCharEncodingHandlerPtr encoder);
 #endif
 
diff --git a/include/private/memory.h b/include/private/memory.h
index 273447fb..ef0497c6 100644
--- a/include/private/memory.h
+++ b/include/private/memory.h
@@ -1,7 +1,9 @@
 #ifndef XML_MEMORY_H_PRIVATE__
 #define XML_MEMORY_H_PRIVATE__
 
-void xmlInitMemoryInternal(void);
-void xmlCleanupMemoryInternal(void);
+XML_HIDDEN void
+xmlInitMemoryInternal(void);
+XML_HIDDEN void
+xmlCleanupMemoryInternal(void);
 
 #endif /* XML_MEMORY_H_PRIVATE__ */
diff --git a/include/private/parser.h b/include/private/parser.h
index 1bf9ee35..43945f9e 100644
--- a/include/private/parser.h
+++ b/include/private/parser.h
@@ -17,9 +17,11 @@
  */
 #define XML_VCTXT_USE_PCTXT (1u << 1)
 
-void xmlErrMemory(xmlParserCtxtPtr ctxt, const char *extra);
-void __xmlErrEncoding(xmlParserCtxtPtr ctxt, xmlParserErrors xmlerr,
-                      const char *msg, const xmlChar *str1,
-                      const xmlChar *str2) LIBXML_ATTR_FORMAT(3,0);
+XML_HIDDEN void
+xmlErrMemory(xmlParserCtxtPtr ctxt, const char *extra);
+XML_HIDDEN void
+__xmlErrEncoding(xmlParserCtxtPtr ctxt, xmlParserErrors xmlerr,
+                 const char *msg, const xmlChar *str1,
+                 const xmlChar *str2) LIBXML_ATTR_FORMAT(3,0);
 
 #endif /* XML_PARSER_H_PRIVATE__ */
diff --git a/include/private/regexp.h b/include/private/regexp.h
index 3ffb378a..f2024939 100644
--- a/include/private/regexp.h
+++ b/include/private/regexp.h
@@ -3,6 +3,7 @@
 
 #include <libxml/xmlautomata.h>
 
-void xmlAutomataSetFlags(xmlAutomataPtr am, int flags);
+XML_HIDDEN void
+xmlAutomataSetFlags(xmlAutomataPtr am, int flags);
 
 #endif /* XML_REGEXP_H_PRIVATE__ */
diff --git a/include/private/save.h b/include/private/save.h
index ec970851..873aad76 100644
--- a/include/private/save.h
+++ b/include/private/save.h
@@ -6,9 +6,11 @@
 
 #ifdef LIBXML_OUTPUT_ENABLED
 
-void xmlBufAttrSerializeTxtContent(xmlBufPtr buf, xmlDocPtr doc,
-                                   xmlAttrPtr attr, const xmlChar * string);
-void xmlNsListDumpOutput(xmlOutputBufferPtr buf, xmlNsPtr cur);
+XML_HIDDEN void
+xmlBufAttrSerializeTxtContent(xmlBufPtr buf, xmlDocPtr doc,
+                              xmlAttrPtr attr, const xmlChar * string);
+XML_HIDDEN void
+xmlNsListDumpOutput(xmlOutputBufferPtr buf, xmlNsPtr cur);
 
 #endif /* LIBXML_OUTPUT_ENABLED */
 
diff --git a/include/private/string.h b/include/private/string.h
index 0c4bf541..9665fc47 100644
--- a/include/private/string.h
+++ b/include/private/string.h
@@ -3,6 +3,7 @@
 
 #include <libxml/xmlstring.h>
 
-xmlChar *xmlEscapeFormatString(xmlChar **msg);
+XML_HIDDEN xmlChar *
+xmlEscapeFormatString(xmlChar **msg);
 
 #endif /* XML_STRING_H_PRIVATE__ */
diff --git a/include/private/threads.h b/include/private/threads.h
index efb64cf0..b337bfa0 100644
--- a/include/private/threads.h
+++ b/include/private/threads.h
@@ -30,14 +30,21 @@ struct _xmlMutex {
 #endif
 };
 
-void __xmlGlobalInitMutexLock(void);
-void __xmlGlobalInitMutexUnlock(void);
-void __xmlGlobalInitMutexDestroy(void);
+XML_HIDDEN void
+__xmlGlobalInitMutexLock(void);
+XML_HIDDEN void
+__xmlGlobalInitMutexUnlock(void);
+XML_HIDDEN void
+__xmlGlobalInitMutexDestroy(void);
 
-void xmlInitThreadsInternal(void);
-void xmlCleanupThreadsInternal(void);
+XML_HIDDEN void
+xmlInitThreadsInternal(void);
+XML_HIDDEN void
+xmlCleanupThreadsInternal(void);
 
-void xmlInitMutex(xmlMutexPtr mutex);
-void xmlCleanupMutex(xmlMutexPtr mutex);
+XML_HIDDEN void
+xmlInitMutex(xmlMutexPtr mutex);
+XML_HIDDEN void
+xmlCleanupMutex(xmlMutexPtr mutex);
 
 #endif /* XML_THREADS_H_PRIVATE__ */
diff --git a/include/private/tree.h b/include/private/tree.h
index e5fd83ba..fb5e1623 100644
--- a/include/private/tree.h
+++ b/include/private/tree.h
@@ -6,12 +6,13 @@
  * node creation/destruction. It avoids spending a lot of time in locking
  * function while checking if the callback exists.
  */
-extern int __xmlRegisterCallbacks;
+XML_HIDDEN extern int
+__xmlRegisterCallbacks;
 
-xmlNodePtr
+XML_HIDDEN xmlNodePtr
 xmlStaticCopyNode(xmlNodePtr node, xmlDocPtr doc, xmlNodePtr parent,
                   int extended);
-xmlNodePtr
+XML_HIDDEN xmlNodePtr
 xmlStaticCopyNodeList(xmlNodePtr node, xmlDocPtr doc, xmlNodePtr parent);
 
 #endif /* XML_TREE_H_PRIVATE__ */
diff --git a/include/private/xinclude.h b/include/private/xinclude.h
index ef9b0f02..abd0dc01 100644
--- a/include/private/xinclude.h
+++ b/include/private/xinclude.h
@@ -3,6 +3,7 @@
 
 #include <libxml/xinclude.h>
 
-int xmlXIncludeSetStreamingMode(xmlXIncludeCtxtPtr ctxt, int mode);
+XML_HIDDEN int
+xmlXIncludeSetStreamingMode(xmlXIncludeCtxtPtr ctxt, int mode);
 
 #endif /* XML_IO_H_PRIVATE__ */
diff --git a/include/private/xpath.h b/include/private/xpath.h
index 52b29745..0e8d7525 100644
--- a/include/private/xpath.h
+++ b/include/private/xpath.h
@@ -1,6 +1,7 @@
 #ifndef XML_XPATH_H_PRIVATE__
 #define XML_XPATH_H_PRIVATE__
 
-void xmlInitXPathInternal(void);
+XML_HIDDEN void
+xmlInitXPathInternal(void);
 
 #endif /* XML_XPATH_H_PRIVATE__ */
diff --git a/include/private/xzlib.h b/include/private/xzlib.h
index 001854e5..b3326980 100644
--- a/include/private/xzlib.h
+++ b/include/private/xzlib.h
@@ -16,11 +16,16 @@
 
 typedef void *xzFile;           /* opaque lzma file descriptor */
 
-xzFile __libxml2_xzopen(const char *path, const char *mode);
-xzFile __libxml2_xzdopen(int fd, const char *mode);
-int __libxml2_xzread(xzFile file, void *buf, unsigned len);
-int __libxml2_xzclose(xzFile file);
-int __libxml2_xzcompressed(xzFile f);
+XML_HIDDEN xzFile
+__libxml2_xzopen(const char *path, const char *mode);
+XML_HIDDEN xzFile
+__libxml2_xzdopen(int fd, const char *mode);
+XML_HIDDEN int
+__libxml2_xzread(xzFile file, void *buf, unsigned len);
+XML_HIDDEN int
+__libxml2_xzclose(xzFile file);
+XML_HIDDEN int
+__libxml2_xzcompressed(xzFile f);
 
 #endif /* LIBXML_LZMA_ENABLED */
 
diff --git a/libxml.h b/libxml.h
index 59294473..5e881e97 100644
--- a/libxml.h
+++ b/libxml.h
@@ -54,6 +54,15 @@ int vfprintf(FILE *, const char *, va_list);
 #include "trio.h"
 #endif
 
+#if !defined(_WIN32) && \
+    !defined(__CYGWIN__) && \
+    (defined(__clang__) || \
+     (defined(__GNUC__) && (__GNUC__ >= 4)))
+#define XML_HIDDEN __attribute__((visibility("hidden")))
+#else
+#define XML_HIDDEN
+#endif
+
 #if defined(__clang__) || \
     (defined(__GNUC__) && (__GNUC__ >= 8))
 #define ATTRIBUTE_NO_SANITIZE(arg) __attribute__((no_sanitize(arg)))