diff --git a/Modules/_decimal/libmpdec/basearith.h b/Modules/_decimal/libmpdec/basearith.h
--- a/Modules/_decimal/libmpdec/basearith.h
+++ b/Modules/_decimal/libmpdec/basearith.h
@@ -35,6 +35,7 @@
 #include "typearith.h"
 
 
+_Pragma(MPD_VISIBILITY_HIDDEN_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);
@@ -207,6 +208,7 @@
     }
     return 1;
 }
+_Pragma(MPD_VISIBILITY_HIDDEN_END)
 
 
 #endif /* BASEARITH_H */
diff --git a/Modules/_decimal/libmpdec/constants.h b/Modules/_decimal/libmpdec/constants.h
--- a/Modules/_decimal/libmpdec/constants.h
+++ b/Modules/_decimal/libmpdec/constants.h
@@ -60,6 +60,7 @@
   #define SIZE3_NTT(x0, x1, x2, w3table) std_size3_ntt(x0, x1, x2, w3table, umod)
 #endif
 
+_Pragma(MPD_VISIBILITY_HIDDEN_START)
 /* PentiumPro (or later) gcc inline asm */
 extern const float MPD_TWO63;
 extern const uint32_t mpd_invmoduli[3][3];
@@ -75,6 +76,7 @@
 extern const mpd_uint_t INV_P1P2_MOD_P3;
 extern const mpd_uint_t LH_P1P2;
 extern const mpd_uint_t UH_P1P2;
+_Pragma(MPD_VISIBILITY_HIDDEN_END)
 
 
 #endif /* CONSTANTS_H */
diff --git a/Modules/_decimal/libmpdec/convolute.h b/Modules/_decimal/libmpdec/convolute.h
--- a/Modules/_decimal/libmpdec/convolute.h
+++ b/Modules/_decimal/libmpdec/convolute.h
@@ -36,8 +36,10 @@
 #define SIX_STEP_THRESHOLD 4096
 
 
+_Pragma(MPD_VISIBILITY_HIDDEN_START)
 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);
+_Pragma(MPD_VISIBILITY_HIDDEN_END)
 
 
 #endif
diff --git a/Modules/_decimal/libmpdec/crt.h b/Modules/_decimal/libmpdec/crt.h
--- a/Modules/_decimal/libmpdec/crt.h
+++ b/Modules/_decimal/libmpdec/crt.h
@@ -34,7 +34,9 @@
 #include <stdio.h>
 
 
+_Pragma(MPD_VISIBILITY_HIDDEN_START)
 void crt3(mpd_uint_t *x1, mpd_uint_t *x2, mpd_uint_t *x3, mpd_size_t nmemb);
+_Pragma(MPD_VISIBILITY_HIDDEN_END)
 
 
 #endif
diff --git a/Modules/_decimal/libmpdec/difradix2.h b/Modules/_decimal/libmpdec/difradix2.h
--- a/Modules/_decimal/libmpdec/difradix2.h
+++ b/Modules/_decimal/libmpdec/difradix2.h
@@ -35,7 +35,9 @@
 #include "numbertheory.h"
 
 
+_Pragma(MPD_VISIBILITY_HIDDEN_START)
 void fnt_dif2(mpd_uint_t a[], mpd_size_t n, struct fnt_params *tparams);
+_Pragma(MPD_VISIBILITY_HIDDEN_END)
 
 
 #endif
diff --git a/Modules/_decimal/libmpdec/fnt.h b/Modules/_decimal/libmpdec/fnt.h
--- a/Modules/_decimal/libmpdec/fnt.h
+++ b/Modules/_decimal/libmpdec/fnt.h
@@ -34,8 +34,10 @@
 #include <stdio.h>
 
 
+_Pragma(MPD_VISIBILITY_HIDDEN_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);
+_Pragma(MPD_VISIBILITY_HIDDEN_END)
 
 
 #endif
diff --git a/Modules/_decimal/libmpdec/fourstep.h b/Modules/_decimal/libmpdec/fourstep.h
--- a/Modules/_decimal/libmpdec/fourstep.h
+++ b/Modules/_decimal/libmpdec/fourstep.h
@@ -34,8 +34,10 @@
 #include <stdio.h>
 
 
+_Pragma(MPD_VISIBILITY_HIDDEN_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);
+_Pragma(MPD_VISIBILITY_HIDDEN_END)
 
 
 #endif
diff --git a/Modules/_decimal/libmpdec/io.c b/Modules/_decimal/libmpdec/io.c
--- a/Modules/_decimal/libmpdec/io.c
+++ b/Modules/_decimal/libmpdec/io.c
@@ -741,6 +741,7 @@
     return -1;
 }
 
+_Pragma(MPD_VISIBILITY_HIDDEN_START)
 int
 mpd_validate_lconv(mpd_spec_t *spec)
 {
@@ -763,6 +764,7 @@
 
     return 0;
 }
+_Pragma(MPD_VISIBILITY_HIDDEN_END)
 
 int
 mpd_parse_fmt_str(mpd_spec_t *spec, const char *fmt, int caps)
diff --git a/Modules/_decimal/libmpdec/mpdecimal.c b/Modules/_decimal/libmpdec/mpdecimal.c
--- a/Modules/_decimal/libmpdec/mpdecimal.c
+++ b/Modules/_decimal/libmpdec/mpdecimal.c
@@ -5008,6 +5008,7 @@
     mpd_qfinalize(result, ctx, status);
 }
 
+_Pragma(MPD_VISIBILITY_HIDDEN_START)
 /* Minimum space needed for the result array in _karatsuba_rec(). */
 static inline mpd_size_t
 _kmul_resultsize(mpd_size_t la, mpd_size_t lb)
@@ -5463,6 +5464,7 @@
     if (w) mpd_free(w);
     return result;
 }
+_Pragma(MPD_VISIBILITY_HIDDEN_END)
 
 
 /* Deal with the special cases of multiplying infinities. */
diff --git a/Modules/_decimal/libmpdec/mpdecimal.h b/Modules/_decimal/libmpdec/mpdecimal.h
--- a/Modules/_decimal/libmpdec/mpdecimal.h
+++ b/Modules/_decimal/libmpdec/mpdecimal.h
@@ -46,6 +46,10 @@
 #include <limits.h>
 #include <assert.h>
 
+#ifndef _Pragma
+  #define _Pragma(x)
+#endif
+
 #ifdef _MSC_VER
   #include "vccompat.h"
   #ifndef UNUSED
@@ -64,8 +68,12 @@
   #endif
   #if defined(__GNUC__) && !defined(__INTEL_COMPILER)
     #define UNUSED __attribute__((unused))
+    #define MPD_VISIBILITY_HIDDEN_START "GCC visibility push(hidden)"
+    #define MPD_VISIBILITY_HIDDEN_END "GCC visibility pop"
   #else
     #define UNUSED
+    #define MPD_VISIBILITY_HIDDEN_START ""
+    #define MPD_VISIBILITY_HIDDEN_END ""
   #endif
   #define EXTINLINE
 #endif
diff --git a/Modules/_decimal/libmpdec/numbertheory.h b/Modules/_decimal/libmpdec/numbertheory.h
--- a/Modules/_decimal/libmpdec/numbertheory.h
+++ b/Modules/_decimal/libmpdec/numbertheory.h
@@ -43,9 +43,11 @@
 };
 
 
+_Pragma(MPD_VISIBILITY_HIDDEN_START)
 mpd_uint_t _mpd_getkernel(mpd_uint_t n, int sign, int modnum);
 struct fnt_params *_mpd_init_fnt_params(mpd_size_t n, int sign, int modnum);
 void _mpd_init_w3table(mpd_uint_t w3table[3], int sign, int modnum);
+_Pragma(MPD_VISIBILITY_HIDDEN_END)
 
 
 #ifdef PPRO
diff --git a/Modules/_decimal/libmpdec/sixstep.h b/Modules/_decimal/libmpdec/sixstep.h
--- a/Modules/_decimal/libmpdec/sixstep.h
+++ b/Modules/_decimal/libmpdec/sixstep.h
@@ -34,8 +34,10 @@
 #include <stdio.h>
 
 
+_Pragma(MPD_VISIBILITY_HIDDEN_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);
+_Pragma(MPD_VISIBILITY_HIDDEN_END)
 
 
 #endif
diff --git a/Modules/_decimal/libmpdec/transpose.h b/Modules/_decimal/libmpdec/transpose.h
--- a/Modules/_decimal/libmpdec/transpose.h
+++ b/Modules/_decimal/libmpdec/transpose.h
@@ -37,9 +37,11 @@
 enum {FORWARD_CYCLE, BACKWARD_CYCLE};
 
 
+_Pragma(MPD_VISIBILITY_HIDDEN_START)
 void std_trans(mpd_uint_t dest[], mpd_uint_t src[], mpd_size_t rows, mpd_size_t cols);
 int transpose_pow2(mpd_uint_t *matrix, mpd_size_t rows, mpd_size_t cols);
 void transpose_3xpow2(mpd_uint_t *matrix, mpd_size_t rows, mpd_size_t cols);
+_Pragma(MPD_VISIBILITY_HIDDEN_END)
 
 
 static inline void pointerswap(mpd_uint_t **a, mpd_uint_t **b)