diff --git a/Modules/_decimal/libmpdec/basearith.h b/Modules/_decimal/libmpdec/basearith.h
index 5004b2c0382..114cef38603 100644
--- a/Modules/_decimal/libmpdec/basearith.h
+++ b/Modules/_decimal/libmpdec/basearith.h
@@ -35,6 +35,10 @@
 #include "typearith.h"
 
 
+/* Internal header file: all symbols have local scope in the DSO */
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_START)
+
+
 mpd_uint_t _mpd_baseadd(mpd_uint_t *w, const mpd_uint_t *u, const mpd_uint_t *v,
                         mpd_size_t m, mpd_size_t n);
 void _mpd_baseaddto(mpd_uint_t *w, const mpd_uint_t *u, mpd_size_t n);
@@ -209,6 +213,9 @@ _mpd_isallnine(const mpd_uint_t *data, mpd_ssize_t len)
 }
 
 
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_END) /* restore previous scope rules */
+
+
 #endif /* BASEARITH_H */
 
 
diff --git a/Modules/_decimal/libmpdec/constants.h b/Modules/_decimal/libmpdec/constants.h
index 2d63d7e3c82..13df9202123 100644
--- a/Modules/_decimal/libmpdec/constants.h
+++ b/Modules/_decimal/libmpdec/constants.h
@@ -33,6 +33,10 @@
 #include "mpdecimal.h"
 
 
+/* Internal header file: all symbols have local scope in the DSO */
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_START)
+
+
 /* choice of optimized functions */
 #if defined(CONFIG_64)
 /* x64 */
@@ -77,6 +81,9 @@ extern const mpd_uint_t LH_P1P2;
 extern const mpd_uint_t UH_P1P2;
 
 
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_END) /* restore previous scope rules */
+
+
 #endif /* CONSTANTS_H */
 
 
diff --git a/Modules/_decimal/libmpdec/convolute.h b/Modules/_decimal/libmpdec/convolute.h
index 2f8d6d831b6..c35ed461d3b 100644
--- a/Modules/_decimal/libmpdec/convolute.h
+++ b/Modules/_decimal/libmpdec/convolute.h
@@ -33,11 +33,18 @@
 #include "mpdecimal.h"
 #include <stdio.h>
 
-#define SIX_STEP_THRESHOLD 4096
 
+/* Internal header file: all symbols have local scope in the DSO */
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_START)
+
+
+#define SIX_STEP_THRESHOLD 4096
 
 int fnt_convolute(mpd_uint_t *c1, mpd_uint_t *c2, mpd_size_t n, int modnum);
 int fnt_autoconvolute(mpd_uint_t *c1, mpd_size_t n, int modnum);
 
 
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_END) /* restore previous scope rules */
+
+
 #endif
diff --git a/Modules/_decimal/libmpdec/crt.h b/Modules/_decimal/libmpdec/crt.h
index 0e03e5d0771..8909232231a 100644
--- a/Modules/_decimal/libmpdec/crt.h
+++ b/Modules/_decimal/libmpdec/crt.h
@@ -34,7 +34,14 @@
 #include <stdio.h>
 
 
+/* Internal header file: all symbols have local scope in the DSO */
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_START)
+
+
 void crt3(mpd_uint_t *x1, mpd_uint_t *x2, mpd_uint_t *x3, mpd_size_t nmemb);
 
 
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_END) /* restore previous scope rules */
+
+
 #endif
diff --git a/Modules/_decimal/libmpdec/difradix2.h b/Modules/_decimal/libmpdec/difradix2.h
index 759442a2bcf..81aa598543f 100644
--- a/Modules/_decimal/libmpdec/difradix2.h
+++ b/Modules/_decimal/libmpdec/difradix2.h
@@ -35,7 +35,14 @@
 #include "numbertheory.h"
 
 
+/* Internal header file: all symbols have local scope in the DSO */
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_START)
+
+
 void fnt_dif2(mpd_uint_t a[], mpd_size_t n, struct fnt_params *tparams);
 
 
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_END) /* restore previous scope rules */
+
+
 #endif
diff --git a/Modules/_decimal/libmpdec/fnt.h b/Modules/_decimal/libmpdec/fnt.h
index 2d701b6c8aa..1f302cccbfa 100644
--- a/Modules/_decimal/libmpdec/fnt.h
+++ b/Modules/_decimal/libmpdec/fnt.h
@@ -34,9 +34,16 @@
 #include <stdio.h>
 
 
+/* Internal header file: all symbols have local scope in the DSO */
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_START)
+
+
 int std_fnt(mpd_uint_t a[], mpd_size_t n, int modnum);
 int std_inv_fnt(mpd_uint_t a[], mpd_size_t n, int modnum);
 
 
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_END) /* restore previous scope rules */
+
+
 #endif
 
diff --git a/Modules/_decimal/libmpdec/fourstep.h b/Modules/_decimal/libmpdec/fourstep.h
index 61d9d6a71a8..593f27d489f 100644
--- a/Modules/_decimal/libmpdec/fourstep.h
+++ b/Modules/_decimal/libmpdec/fourstep.h
@@ -34,8 +34,15 @@
 #include <stdio.h>
 
 
+/* Internal header file: all symbols have local scope in the DSO */
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_START)
+
+
 int four_step_fnt(mpd_uint_t *a, mpd_size_t n, int modnum);
 int inv_four_step_fnt(mpd_uint_t *a, mpd_size_t n, int modnum);
 
 
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_END) /* restore previous scope rules */
+
+
 #endif
diff --git a/Modules/_decimal/libmpdec/memory.h b/Modules/_decimal/libmpdec/memory.h
index b3a4a56e968..7e73c130593 100644
--- a/Modules/_decimal/libmpdec/memory.h
+++ b/Modules/_decimal/libmpdec/memory.h
@@ -33,11 +33,18 @@
 #include "mpdecimal.h"
 
 
+/* Internal header file: all symbols have local scope in the DSO */
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_START)
+
+
 int mpd_switch_to_dyn(mpd_t *result, mpd_ssize_t size, uint32_t *status);
 int mpd_switch_to_dyn_zero(mpd_t *result, mpd_ssize_t size, uint32_t *status);
 int mpd_realloc_dyn(mpd_t *result, mpd_ssize_t size, uint32_t *status);
 
 
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_END) /* restore previous scope rules */
+
+
 #endif
 
 
diff --git a/Modules/_decimal/libmpdec/mpdecimal.h b/Modules/_decimal/libmpdec/mpdecimal.h
index d131c71441f..f5affdbc5e8 100644
--- a/Modules/_decimal/libmpdec/mpdecimal.h
+++ b/Modules/_decimal/libmpdec/mpdecimal.h
@@ -67,10 +67,24 @@ extern "C" {
   #else
     #define UNUSED
   #endif
+  #if defined(__GNUC__) && __GNUC__ >= 4 && !defined(__INTEL_COMPILER)
+    #define MPD_PRAGMA(x) _Pragma(x)
+    #define MPD_HIDE_SYMBOLS_START "GCC visibility push(hidden)"
+    #define MPD_HIDE_SYMBOLS_END "GCC visibility pop"
+  #else
+    #define MPD_PRAGMA(x)
+    #define MPD_HIDE_SYMBOLS_START
+    #define MPD_HIDE_SYMBOLS_END
+  #endif
   #define EXTINLINE
 #endif
 
 
+/* This header file is internal for the purpose of building _decimal.so.
+ * All symbols should have local scope in the DSO. */
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_START)
+
+
 #if !defined(LEGACY_COMPILER)
   #if !defined(UINT64_MAX)
     /* The following #error is just a warning. If the compiler indeed does
@@ -789,6 +803,9 @@ int mpd_resize(mpd_t *result, mpd_ssize_t size, mpd_context_t *ctx);
 int mpd_resize_zero(mpd_t *result, mpd_ssize_t size, mpd_context_t *ctx);
 
 
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_END) /* restore previous scope rules */
+
+
 #ifdef __cplusplus
 } /* END extern "C" */
 #endif
diff --git a/Modules/_decimal/libmpdec/numbertheory.h b/Modules/_decimal/libmpdec/numbertheory.h
index f54d11dc382..10922546198 100644
--- a/Modules/_decimal/libmpdec/numbertheory.h
+++ b/Modules/_decimal/libmpdec/numbertheory.h
@@ -34,6 +34,10 @@
 #include "mpdecimal.h"
 
 
+/* Internal header file: all symbols have local scope in the DSO */
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_START)
+
+
 /* transform parameters */
 struct fnt_params {
     int modnum;
@@ -66,6 +70,9 @@ std_setmodulus(int modnum, mpd_uint_t *umod)
 #endif
 
 
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_END) /* restore previous scope rules */
+
+
 #endif
 
 
diff --git a/Modules/_decimal/libmpdec/sixstep.h b/Modules/_decimal/libmpdec/sixstep.h
index 4d251df0595..0467007061b 100644
--- a/Modules/_decimal/libmpdec/sixstep.h
+++ b/Modules/_decimal/libmpdec/sixstep.h
@@ -34,8 +34,15 @@
 #include <stdio.h>
 
 
+/* Internal header file: all symbols have local scope in the DSO */
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_START)
+
+
 int six_step_fnt(mpd_uint_t *a, mpd_size_t n, int modnum);
 int inv_six_step_fnt(mpd_uint_t *a, mpd_size_t n, int modnum);
 
 
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_END) /* restore previous scope rules */
+
+
 #endif
diff --git a/Modules/_decimal/libmpdec/transpose.h b/Modules/_decimal/libmpdec/transpose.h
index dd0aec66007..7e349ee08df 100644
--- a/Modules/_decimal/libmpdec/transpose.h
+++ b/Modules/_decimal/libmpdec/transpose.h
@@ -34,6 +34,10 @@
 #include <stdio.h>
 
 
+/* Internal header file: all symbols have local scope in the DSO */
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_START)
+
+
 enum {FORWARD_CYCLE, BACKWARD_CYCLE};
 
 
@@ -52,4 +56,7 @@ static inline void pointerswap(mpd_uint_t **a, mpd_uint_t **b)
 }
 
 
+MPD_PRAGMA(MPD_HIDE_SYMBOLS_END) /* restore previous scope rules */
+
+
 #endif