diff --git a/libstdc++-v3/src/c++17/ryu/LOCAL_PATCHES b/libstdc++-v3/src/c++17/ryu/LOCAL_PATCHES
index 51e504cb6ea..011626f07e2 100644
--- a/libstdc++-v3/src/c++17/ryu/LOCAL_PATCHES
+++ b/libstdc++-v3/src/c++17/ryu/LOCAL_PATCHES
@@ -1,2 +1,3 @@
 r11-6248
 r11-7636
+r12-725
diff --git a/libstdc++-v3/src/c++17/ryu/ryu_generic_128.h b/libstdc++-v3/src/c++17/ryu/ryu_generic_128.h
index 2afbf274e11..6d988ab01eb 100644
--- a/libstdc++-v3/src/c++17/ryu/ryu_generic_128.h
+++ b/libstdc++-v3/src/c++17/ryu/ryu_generic_128.h
@@ -18,9 +18,9 @@
 #define RYU_GENERIC_128_H
 
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+// NOTE: These symbols are declared extern "C" upstream, but we don't want that
+// because it'd override the internal linkage of the anonymous namespace into
+// which this header is included.
 
 // This is a generic 128-bit implementation of float to shortest conversion
 // using the Ryu algorithm. It can handle any IEEE-compatible floating-point
@@ -42,18 +42,6 @@ struct floating_decimal_128 {
   bool sign;
 };
 
-struct floating_decimal_128 float_to_fd128(float f);
-struct floating_decimal_128 double_to_fd128(double d);
-
-// According to wikipedia (https://en.wikipedia.org/wiki/Long_double), this likely only works on
-// x86 with specific compilers (clang?). May need an ifdef.
-struct floating_decimal_128 long_double_to_fd128(long double d);
-
-// Converts the given binary floating point number to the shortest decimal floating point number
-// that still accurately represents it.
-struct floating_decimal_128 generic_binary_to_decimal(
-    const uint128_t bits, const uint32_t mantissaBits, const uint32_t exponentBits, const bool explicitLeadingBit);
-
 // Converts the given decimal floating point number to a string, writing to result, and returning
 // the number characters written. Does not terminate the buffer with a 0. In the worst case, this
 // function can write up to 53 characters.
@@ -63,8 +51,5 @@ struct floating_decimal_128 generic_binary_to_decimal(
 // = 1 + 39 + 1 + 1 + 1 + 10 = 53
 int generic_to_chars(const struct floating_decimal_128 v, char* const result);
 
-#ifdef __cplusplus
-}
-#endif
 
 #endif // RYU_GENERIC_128_H
diff --git a/libstdc++-v3/testsuite/20_util/to_chars/4.cc b/libstdc++-v3/testsuite/20_util/to_chars/4.cc
new file mode 100644
index 00000000000..00781ee6379
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/to_chars/4.cc
@@ -0,0 +1,36 @@
+// Copyright (C) 2021 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do link { target c++17 } }
+// { dg-require-effective-target ieee-floats }
+// { dg-require-static-libstdcxx }
+// { dg-additional-options "-static-libstdc++" }
+
+// Verify the Ryu symbol generic_to_chars doesn't inadvertently leak into
+// libstdc++.a.  If it did, this test would fail at link time with a multiple
+// definition error.
+
+#include <charconv>
+
+extern "C" void generic_to_chars(void) { }
+
+int
+main()
+{
+  char x[64];
+  std::to_chars(x, x+64, 42.L, std::chars_format::scientific);
+}