diff --git a/.travis.yml b/.travis.yml
index 5dcd81a2..41a52d19 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -5,10 +5,12 @@ addons:
     packages:
       - autoconf
       - automake
+      - clang
       - gawk
+      - gcc-10
       - lcov
       - libtool
-      - llvm
+      - llvm-dev
       - pkg-config
       - python3-venv
       - valgrind
@@ -84,6 +86,20 @@ matrix:
       env:
         - CONF="--enable-obsolete-api --enable-hashes=all"
         - SANITIZER=1
+    - name: "Linux, GCC, all hashes, obsolete API, LTO, ASan+UBSan"
+      compiler: gcc
+      os: linux
+      env:
+        - CONF="--enable-obsolete-api --enable-hashes=all"
+        - LTO=1
+        - SANITIZER=1
+    - name: "Linux, Clang, all hashes, obsolete API, LTO, ASan+UBSan"
+      compiler: clang
+      os: linux
+      env:
+        - CONF="--enable-obsolete-api --enable-hashes=all"
+        - LTO=1
+        - SANITIZER=1
     - name: "Linux, GCC, all hashes, static lib"
       compiler: gcc
       os: linux
diff --git a/.travis_script.sh b/.travis_script.sh
index d3af788c..146a8045 100755
--- a/.travis_script.sh
+++ b/.travis_script.sh
@@ -133,6 +133,29 @@ if [[ "$SANITIZER" == "1" ]]; then
   export CXXFLAGS="$CXXFLAGS -fsanitize=undefined,address"
 fi
 
+if [[ "$LTO" == "1" ]]; then
+  if [[ "$CC" == "gcc" ]]; then
+    export CC="gcc-10"
+    export CPP="cpp-10"
+    export CXX="g++-10"
+    export AR="gcc-ar-10"
+    export NM="gcc-nm-10"
+    export RANLIB="gcc-ranlib-10"
+    export CFLAGS="$CFLAGS -flto=auto -ffat-lto-objects"
+    export CXXFLAGS="$CXXFLAGS -flto=auto -ffat-lto-objects"
+  fi
+  if [[ "$CC" == "clang" ]]; then
+    export CC="/usr/bin/clang"
+    export CPP="/usr/bin/clang-cpp-10"
+    export CXX="/usr/bin/clang++"
+    export AR="/usr/bin/llvm-ar"
+    export NM="/usr/bin/llvm-nm"
+    export RANLIB="/usr/bin/llvm-ranlib"
+    export CFLAGS="$CFLAGS -flto"
+    export CXXFLAGS="$CXXFLAGS -flto"
+  fi
+fi
+
 pushd build
 log_time preparation
 
diff --git a/NEWS b/NEWS
index 67b1aa2b..34839efe 100644
--- a/NEWS
+++ b/NEWS
@@ -17,6 +17,11 @@ Version 4.4.17
   newline '\n' character, since all parameters of the user data must
   be on the same line within the Unix shadow file.
 
+* Building with link-time optimization (-flto) enabled is now
+  possible with either GCC 10 or LLVM/Clang 10 (issue #24).
+  See the 'Portability Notes' section of the README.md file for
+  detailed instructions and possible caveats.
+
 Version 4.4.16
 * Add support for the e2k architecture.
 
diff --git a/README.md b/README.md
index d0197a01..c0a40a63 100644
--- a/README.md
+++ b/README.md
@@ -93,13 +93,29 @@ not always be able to retrieve cryptographically-sound random numbers
 from the operating system; if you call these functions with a null
 pointer for the “rbytes” argument, be prepared for them to fail.
 
-As of mid-2018, GCC and LLVM don’t support link-time optimization of
-libraries that use symbol versioning.  If you build libxcrypt with
-either of these compilers, do not use `-flto`.  See [GCC bug 48200][1]
-for specifics; the problem is very similar for LLVM.  Because this is,
-at its root, a set of missing compiler features, we expect link-time
-optimization won’t work in other C compilers either, but we haven’t
-tested it ourselves.
+As of August 2020, link-time optimization (`-flto`) of libraries that use
+symbol versioning is initially supported by GCC 10 and LLVM/Clang 10, if
+their compiler specific toolchain is used during compilation.
+
+For GCC the needed tools are called with:
+```
+./configure CC="gcc" AR="gcc-ar" NM="gcc-nm" RANLIB="gcc-ranlib" \
+CFLAGS="-O2 -flto -g" ...
+```
+and for LLVM/Clang those tools are called with:
+```
+./configure CC="clang" AR="llvm-ar" NM="llvm-nm" RANLIB="llvm-ranlib" \
+CFLAGS="-O2 -flto -g" ...
+```
+
+To build static libraries, that can be linked against non-LTO objects
+one may also want to add `-ffat-lto-objects` to the CFLAGS.
+
+If you build libxcrypt with earlier versions of these compilers, do not
+use `-flto`.  See [GCC bug 48200][1] for specifics; the problem is very
+similar for LLVM.  Because this is, at its root, a set of missing compiler
+features, we expect link-time optimization won’t work in other C compilers
+either, but we haven’t tested it ourselves.
 
 [1]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48200
 
diff --git a/lib/crypt-port.h b/lib/crypt-port.h
index bec36aca..bbbe92dd 100644
--- a/lib/crypt-port.h
+++ b/lib/crypt-port.h
@@ -50,6 +50,20 @@
 #include <sys/param.h>
 #endif
 
+/* The prototype of the crypt() function possibly defined in <unistd.h>
+   needs to be renamed as it might be incompatible with our declaration.
+   Defining this macro *AFTER* the crypt-symbol-vers header, which also
+   defines the same macro for symbol-versioning purposes, was included,
+   would lead to a clashing redefinition of this macro, and thus cause
+   our symbol-versioning would not work properly.  */
+#ifdef HAVE_UNISTD_H
+#define crypt unistd_crypt_is_incompatible
+#define crypt_r unistd_crypt_r_is_incompatible
+#include <unistd.h>
+#undef crypt
+#undef crypt_r
+#endif
+
 #ifndef HAVE_SYS_CDEFS_THROW
 #define __THROW /* nothing */
 #endif
@@ -179,11 +193,29 @@ _crypt_strcpy_or_abort (void *, const size_t, const void *);
 # define _strong_alias(name, aliasname) \
   extern __typeof (name) aliasname __THROW __attribute__ ((alias (#name)))
 
+/* Starting with GCC 10, we can use the symver attribute, which also works
+   with link-time optimization enabled.  */
+# if __GNUC__ >= 10
+
+/* Set the symbol version for EXTNAME, which uses INTNAME as its
+   implementation.  */
+# define symver_set(extstr, intname, version, mode) \
+  extern __typeof (intname) intname __THROW \
+    __attribute__((symver (extstr mode #version)))
+
+/* Referencing specific _compatibility_ symbols still needs inline asm.  */
+# define _symver_ref(extstr, intname, version) \
+  __asm__ (".symver " #intname "," extstr "@" #version)
+
+# else
+
 /* Set the symbol version for EXTNAME, which uses INTNAME as its
    implementation.  */
 # define symver_set(extstr, intname, version, mode) \
   __asm__ (".symver " #intname "," extstr mode #version)
 
+# endif
+
 #else
 # error "Don't know how to do symbol versioning with this compiler"
 #endif
@@ -239,9 +271,14 @@ _crypt_strcpy_or_abort (void *, const size_t, const void *);
 
 /* Tests may need to _refer_ to compatibility symbols, but should never need
    to _define_ them.  */
-
 #define symver_ref(extstr, intname, version) \
+  _symver_ref(extstr, intname, version)
+
+/* Generic way for referencing specific _compatibility_ symbols.  */
+#ifndef _symver_ref
+#define _symver_ref(extstr, intname, version) \
   symver_set(extstr, intname, version, "@")
+#endif
 
 /* Define configuration macros used during compile-time by the
    GOST R 34.11-2012 "Streebog" hash function.  */
diff --git a/lib/randombytes.c b/lib/randombytes.c
index 2c80bc7d..f7af93d4 100644
--- a/lib/randombytes.c
+++ b/lib/randombytes.c
@@ -31,9 +31,6 @@
 #ifdef HAVE_SYS_STAT_H
 #include <sys/stat.h>
 #endif
-#ifdef HAVE_UNISTD_H
-#include <unistd.h>
-#endif
 
 /* If we have O_CLOEXEC, we use it, but if we don't, we don't worry
    about it.  */
diff --git a/libxcrypt.spec.rpkg b/libxcrypt.spec.rpkg
index 12e24426..e8ecf883 100644
--- a/libxcrypt.spec.rpkg
+++ b/libxcrypt.spec.rpkg
@@ -151,11 +151,6 @@ fi                                          \
 %global _ld_strict_symbol_defs 1
 
 
-# The library uses symbol versioning in way
-# that is not compatible with LTO currently.
-%undefine _lto_cflags
-
-
 Name:           {{{ git_name }}}
 Version:        {{{ git_real_version }}}
 Release:        0.{{{ git_real_release }}}%{?dist}
diff --git a/test/badsalt.c b/test/badsalt.c
index 803b5758..2eecc19c 100644
--- a/test/badsalt.c
+++ b/test/badsalt.c
@@ -17,12 +17,10 @@
    <http://www.gnu.org/licenses/>.  */
 
 #include "crypt-port.h"
-#include <crypt.h>
 #include <errno.h>
 #include <stdio.h>
 #include <string.h>
 #include <sys/mman.h>
-#include <unistd.h>
 
 static const char phrase[] = "values of β will give rise to dom!";
 
diff --git a/test/crypt-badargs.c b/test/crypt-badargs.c
index 59c6690a..ae690320 100644
--- a/test/crypt-badargs.c
+++ b/test/crypt-badargs.c
@@ -15,7 +15,6 @@
 #include <string.h>
 #include <signal.h>
 #include <sys/mman.h>
-#include <unistd.h>
 
 /* The behavior tested below should be consistent for all hashing
    methods.  */
diff --git a/test/getrandom-fallbacks.c b/test/getrandom-fallbacks.c
index 9f93cbad..8469a2ec 100644
--- a/test/getrandom-fallbacks.c
+++ b/test/getrandom-fallbacks.c
@@ -23,9 +23,6 @@
 #ifdef HAVE_SYS_STAT_H
 #include <sys/stat.h>
 #endif
-#ifdef HAVE_UNISTD_H
-#include <unistd.h>
-#endif
 
 /* If arc4random_buf is available, all of the fallback logic is compiled
    out and this test is unnecessary.  If ld --wrap is not available this
diff --git a/test/getrandom-interface.c b/test/getrandom-interface.c
index 82be78af..e0336872 100644
--- a/test/getrandom-interface.c
+++ b/test/getrandom-interface.c
@@ -15,7 +15,6 @@
 #include <string.h>
 #include <signal.h>
 #include <sys/mman.h>
-#include <unistd.h>
 
 static bool error_occurred;
 
diff --git a/test/short-outbuf.c b/test/short-outbuf.c
index 9418c2a7..be274311 100644
--- a/test/short-outbuf.c
+++ b/test/short-outbuf.c
@@ -17,7 +17,6 @@
  */
 
 #include "crypt-port.h"
-#include <crypt.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>