diff --git a/doc/xml/release.xml b/doc/xml/release.xml
index 586fb301a..3605db1e6 100644
--- a/doc/xml/release.xml
+++ b/doc/xml/release.xml
@@ -55,6 +55,10 @@
                         <p>Require <proper>S3</proper> key options except for <cmd>local</cmd>/<cmd>remote</cmd> commands.</p>
                     </release-item>
 
+                    <release-item>
+                        <p>Explicitly compile with Posix 2001 standard.</p>
+                    </release-item>
+
                     <release-item>
                         <p>Add <code>ServiceError</code> for errors from a service that can be retried.</p>
                     </release-item>
diff --git a/libc/Makefile.PL b/libc/Makefile.PL
index d87f1dd68..266a37265 100644
--- a/libc/Makefile.PL
+++ b/libc/Makefile.PL
@@ -113,6 +113,7 @@ WriteMakefile
         -Wfatal-errors -Wall -Wextra -Wwrite-strings -Wno-clobbered -Wno-missing-field-initializers
         -o $@
         -std=c99
+        -D_POSIX_C_SOURCE=200112L
         -D_FILE_OFFSET_BITS=64
         `xml2-config --cflags`
     )),
diff --git a/src/Makefile b/src/Makefile
index bb7114b02..4044af398 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -7,8 +7,8 @@
 ####################################################################################################################################
 CC=gcc
 
-# Compile using C99 standard
-CSTD = -std=c99
+# Compile using C99 and Posix 2001 standards
+CSTD = -std=c99 -D_POSIX_C_SOURCE=200112L
 
 # Compile optimizations
 COPT = -O2
diff --git a/src/storage/driver/posix/common.c b/src/storage/driver/posix/common.c
index 8c43d6f83..460612b14 100644
--- a/src/storage/driver/posix/common.c
+++ b/src/storage/driver/posix/common.c
@@ -1,11 +1,6 @@
 /***********************************************************************************************************************************
 Posix Common File Routines
 ***********************************************************************************************************************************/
-// So fsync() will work on older glib versions
-#ifndef _POSIX_C_SOURCE
-    #define _POSIX_C_SOURCE 200112L
-#endif
-
 #include <fcntl.h>
 #include <unistd.h>
 
diff --git a/src/storage/driver/posix/storage.c b/src/storage/driver/posix/storage.c
index 339f2fe0a..7cf339049 100644
--- a/src/storage/driver/posix/storage.c
+++ b/src/storage/driver/posix/storage.c
@@ -1,11 +1,6 @@
 /***********************************************************************************************************************************
 Posix Storage Driver
 ***********************************************************************************************************************************/
-// So lstat() will work on older glib versions
-#ifndef _POSIX_C_SOURCE
-    #define _POSIX_C_SOURCE 200112L
-#endif
-
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
diff --git a/test/lib/pgBackRestTest/Common/JobTest.pm b/test/lib/pgBackRestTest/Common/JobTest.pm
index d1c5e979a..16302772b 100644
--- a/test/lib/pgBackRestTest/Common/JobTest.pm
+++ b/test/lib/pgBackRestTest/Common/JobTest.pm
@@ -383,7 +383,8 @@ sub run
 
                 # Flags that are common to all builds
                 my $strCommonFlags =
-                    '-I. -Itest -std=c99 -fPIC -g -Wno-clobbered `perl -MExtUtils::Embed -e ccopts` -DWITH_PERL' .
+                    '-I. -Itest -std=c99 -fPIC -g -Wno-clobbered -D_POSIX_C_SOURCE=200112L' .
+                        ' `perl -MExtUtils::Embed -e ccopts` -DWITH_PERL' .
                         ' `xml2-config --cflags`' . ($self->{bProfile} ? " -pg" : '') .
                     ($self->{oTest}->{&TEST_DEBUG_UNIT_SUPPRESS} ? '' : " -DDEBUG_UNIT") .
                     (vmWithBackTrace($self->{oTest}->{&TEST_VM}) && $self->{bBackTrace} ? ' -DWITH_BACKTRACE' : '') .