diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 665448c..0a35086 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -12794,8 +12794,9 @@ valid_array_size_p (location_t loc, tree type, tree name)
 /* Read SOURCE_DATE_EPOCH from environment to have a deterministic
    timestamp to replace embedded current dates to get reproducible
    results.  Returns -1 if SOURCE_DATE_EPOCH is not defined.  */
+
 time_t
-get_source_date_epoch ()
+cb_get_source_date_epoch (cpp_reader *pfile ATTRIBUTE_UNUSED)
 {
   char *source_date_epoch;
   long long epoch;
@@ -12807,19 +12808,14 @@ get_source_date_epoch ()
 
   errno = 0;
   epoch = strtoll (source_date_epoch, &endptr, 10);
-  if ((errno == ERANGE && (epoch == LLONG_MAX || epoch == LLONG_MIN))
-      || (errno != 0 && epoch == 0))
-    fatal_error (UNKNOWN_LOCATION, "environment variable $SOURCE_DATE_EPOCH: "
-		 "strtoll: %s\n", xstrerror(errno));
-  if (endptr == source_date_epoch)
-    fatal_error (UNKNOWN_LOCATION, "environment variable $SOURCE_DATE_EPOCH: "
-		 "no digits were found: %s\n", endptr);
-  if (*endptr != '\0')
-    fatal_error (UNKNOWN_LOCATION, "environment variable $SOURCE_DATE_EPOCH: "
-		 "trailing garbage: %s\n", endptr);
-  if (epoch < 0)
-    fatal_error (UNKNOWN_LOCATION, "environment variable $SOURCE_DATE_EPOCH: "
-		 "value must be nonnegative: %lld \n", epoch);
+  if (errno != 0 || endptr == source_date_epoch || *endptr != '\0'
+      || epoch < 0 || epoch > MAX_SOURCE_DATE_EPOCH)
+    {
+      error_at (input_location, "environment variable SOURCE_DATE_EPOCH must "
+	        "expand to a non-negative integer less than or equal to %wd",
+		MAX_SOURCE_DATE_EPOCH);
+      return (time_t) -1;
+    }
 
   return (time_t) epoch;
 }
diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index 0ee9f56..da18d27 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -1088,6 +1088,16 @@ extern vec<tree, va_gc> *make_tree_vector_copy (const vec<tree, va_gc> *);
    c_register_builtin_type.  */
 extern GTY(()) tree registered_builtin_types;
 
+/* Read SOURCE_DATE_EPOCH from environment to have a deterministic
+   timestamp to replace embedded current dates to get reproducible
+   results.  Returns -1 if SOURCE_DATE_EPOCH is not defined.  */
+extern time_t cb_get_source_date_epoch (cpp_reader *pfile);
+
+/* The value (as a unix timestamp) corresponds to date
+   "Dec 31 9999 23:59:59 UTC", which is the latest date that __DATE__ and
+   __TIME__ can store.  */
+#define MAX_SOURCE_DATE_EPOCH 253402300799
+
 /* In c-gimplify.c  */
 extern void c_genericize (tree);
 extern int c_gimplify_expr (tree *, gimple_seq *, gimple_seq *);
@@ -1482,9 +1492,4 @@ extern bool valid_array_size_p (location_t, tree, tree);
 extern bool cilk_ignorable_spawn_rhs_op (tree);
 extern bool cilk_recognize_spawn (tree, tree *);
 
-/* Read SOURCE_DATE_EPOCH from environment to have a deterministic
-   timestamp to replace embedded current dates to get reproducible
-   results.  Returns -1 if SOURCE_DATE_EPOCH is not defined.  */
-extern time_t get_source_date_epoch (void);
-
 #endif /* ! GCC_C_COMMON_H */
diff --git a/gcc/c-family/c-lex.c b/gcc/c-family/c-lex.c
index 38a428d..308e355 100644
--- a/gcc/c-family/c-lex.c
+++ b/gcc/c-family/c-lex.c
@@ -80,6 +80,7 @@ init_c_lex (void)
   cb->valid_pch = c_common_valid_pch;
   cb->read_pch = c_common_read_pch;
   cb->has_attribute = c_common_has_attribute;
+  cb->get_source_date_epoch = cb_get_source_date_epoch;
 
   /* Set the debug callbacks if we can use them.  */
   if ((debug_info_level == DINFO_LEVEL_VERBOSE
@@ -389,9 +390,8 @@ c_lex_with_flags (tree *value, location_t *loc, unsigned char *cpp_flags,
   enum cpp_ttype type;
   unsigned char add_flags = 0;
   enum overflow_type overflow = OT_NONE;
-  time_t source_date_epoch = get_source_date_epoch ();
 
-  cpp_init_source_date_epoch (parse_in, source_date_epoch);
+  cpp_init_source_date_epoch (parse_in);
 
   timevar_push (TV_CPP);
  retry:
diff --git a/gcc/doc/cppenv.texi b/gcc/doc/cppenv.texi
index e958e93..8cefd52 100644
--- a/gcc/doc/cppenv.texi
+++ b/gcc/doc/cppenv.texi
@@ -81,7 +81,6 @@ main input file is omitted.
 @end ifclear
 
 @item SOURCE_DATE_EPOCH
-
 If this variable is set, its value specifies a UNIX timestamp to be
 used in replacement of the current date and time in the @code{__DATE__}
 and @code{__TIME__} macros, so that the embedded timestamps become
@@ -89,8 +88,9 @@ reproducible.
 
 The value of @env{SOURCE_DATE_EPOCH} must be a UNIX timestamp,
 defined as the number of seconds (excluding leap seconds) since
-01 Jan 1970 00:00:00 represented in ASCII, identical to the output of
-@samp{@command{date +%s}}.
+01 Jan 1970 00:00:00 represented in ASCII; identical to the output of
+@samp{@command{date +%s}} on GNU/Linux and other systems that support the
+@code{%s} extension in the @code{date} command.
 
 The value should be a known timestamp such as the last modification
 time of the source or package and it should be set by the build
diff --git a/gcc/gcc.c b/gcc/gcc.c
index 7bcf3b3..58a0b77 100644
--- a/gcc/gcc.c
+++ b/gcc/gcc.c
@@ -3547,6 +3547,32 @@ save_switch (const char *opt, size_t n_args, const char *const *args,
   n_switches++;
 }
 
+/* Set the SOURCE_DATE_EPOCH environment variable to the current time if it is
+   not set already.  */
+
+static void
+set_source_date_epoch_envvar ()
+{
+  /* Array size is 21 = ceil(log_10(2^64)) + 1 to hold string representations
+     of 64 bit integers.  */
+  char source_date_epoch[21];
+  time_t tt;
+  struct tm *tb = NULL;
+
+  errno = 0;
+  tt = time (NULL);
+  if (tt < (time_t) 0 || errno != 0)
+    tt = (time_t) 0;
+
+  tb = gmtime (&tt);
+
+  snprintf (source_date_epoch, 21, "%llu", (unsigned long long) tb);
+  /* Using setenv instead of xputenv because we want the variable to remain
+     after finalizing so that it's still set in the second run when using
+     -fcompare-debug.  */
+  setenv ("SOURCE_DATE_EPOCH", source_date_epoch, 0);
+}
+
 /* Handle an option DECODED that is unknown to the option-processing
    machinery.  */
 
@@ -3846,6 +3872,7 @@ driver_handle_option (struct gcc_options *opts,
       else
 	compare_debug_opt = arg;
       save_switch (compare_debug_replacement_opt, 0, NULL, validated, true);
+      set_source_date_epoch_envvar ();
       return true;
 
     case OPT_fdiagnostics_color_:
diff --git a/gcc/testsuite/gcc.dg/cpp/source_date_epoch-1.c b/gcc/testsuite/gcc.dg/cpp/source_date_epoch-1.c
new file mode 100644
index 0000000..f6aa1a3
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/cpp/source_date_epoch-1.c
@@ -0,0 +1,11 @@
+/* { dg-do run } */
+/* { dg-set-compiler-env-var SOURCE_DATE_EPOCH "630333296" } */
+
+int
+main(void)
+{
+  __builtin_printf ("%s %s\n", __DATE__, __TIME__);
+  return 0;
+}
+
+/* { dg-output "^Dec 22 1989 12:34:56\n$" } */
diff --git a/gcc/testsuite/gcc.dg/cpp/source_date_epoch-2.c b/gcc/testsuite/gcc.dg/cpp/source_date_epoch-2.c
new file mode 100644
index 0000000..4211552
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/cpp/source_date_epoch-2.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-set-compiler-env-var SOURCE_DATE_EPOCH "AAA" } */
+
+int
+main(void)
+{
+  __builtin_printf ("%s %s\n", __DATE__, __TIME__); /* { dg-error "environment variable SOURCE_DATE_EPOCH must expand to a non-negative integer less than or equal to 253402300799" "Invalid SOURCE_DATE_EPOCH not reported" } */
+  __builtin_printf ("%s %s\n", __DATE__, __TIME__); /* { dg-bogus "environment variable SOURCE_DATE_EPOCH must expand to a non-negative integer less than or equal to 253402300799" "Invalid SOURCE_DATE_EPOCH reported twice" }  */
+  return 0;
+}
diff --git a/gcc/testsuite/lib/gcc-dg.exp b/gcc/testsuite/lib/gcc-dg.exp
index 39a7c20..c0c0cc0 100644
--- a/gcc/testsuite/lib/gcc-dg.exp
+++ b/gcc/testsuite/lib/gcc-dg.exp
@@ -451,6 +451,38 @@ proc restore-target-env-var { } {
     }
 }
 
+proc dg-set-compiler-env-var { args } {
+    global set_compiler_env_var
+    global saved_compiler_env_var
+    if { [llength $args] != 3 } {
+	error "dg-set-compiler-env-var: need two arguments"
+	return
+    }
+    set var [lindex $args 1]
+    set value [lindex $args 2]
+    if [info exists ::env($var)] {
+      lappend saved_compiler_env_var [list $var 1 $::env($var)]
+    } else {
+      lappend saved_compiler_env_var [list $var 0]
+    }
+    setenv $var $value
+    lappend set_compiler_env_var [list $var $value]
+}
+
+proc restore-compiler-env-var { } {
+    global saved_compiler_env_var
+    for { set env_vari [llength $saved_compiler_env_var] } {
+          [incr env_vari -1] >= 0 } {} {
+	set env_var [lindex $saved_compiler_env_var $env_vari]
+	set var [lindex $env_var 0]
+	if [lindex $env_var 1] {
+	    setenv $var [lindex $env_var 2]
+	} else {
+	    unsetenv $var
+	}
+    }
+}
+
 # Utility routines.
 
 #
@@ -874,6 +906,10 @@ if { [info procs saved-dg-test] == [list] } {
 	if [info exists set_target_env_var] {
 	    unset set_target_env_var
 	}
+	if [info exists set_compiler_env_var] {
+	    restore-compiler-env-var
+	    unset set_compiler_env_var
+	}
 	if [info exists keep_saved_temps_suffixes] {
 	    unset keep_saved_temps_suffixes
 	}
diff --git a/libcpp/include/cpplib.h b/libcpp/include/cpplib.h
index 4998b3a..12cad78 100644
--- a/libcpp/include/cpplib.h
+++ b/libcpp/include/cpplib.h
@@ -594,6 +594,9 @@ struct cpp_callbacks
 
   /* Callback that can change a user builtin into normal macro.  */
   bool (*user_builtin_macro) (cpp_reader *, cpp_hashnode *);
+
+  /* Callback to parse SOURCE_DATE_EPOCH from environment.  */
+  time_t (*get_source_date_epoch) (cpp_reader *);
 };
 
 #ifdef VMS
@@ -784,8 +787,8 @@ extern void cpp_init_special_builtins (cpp_reader *);
 /* Set up built-ins like __FILE__.  */
 extern void cpp_init_builtins (cpp_reader *, int);
 
-/* Initialize the source_date_epoch value.  */
-extern void cpp_init_source_date_epoch (cpp_reader *, time_t);
+/* Initialize the source_date_epoch value to -2.  */
+extern void cpp_init_source_date_epoch (cpp_reader *);
 
 /* This is called after options have been parsed, and partially
    processed.  */
diff --git a/libcpp/init.c b/libcpp/init.c
index f5ff85b..76ce7d6 100644
--- a/libcpp/init.c
+++ b/libcpp/init.c
@@ -535,9 +535,9 @@ cpp_init_builtins (cpp_reader *pfile, int hosted)
 
 /* Initialize the source_date_epoch value.  */
 void
-cpp_init_source_date_epoch (cpp_reader *pfile, time_t source_date_epoch)
+cpp_init_source_date_epoch (cpp_reader *pfile)
 {
-  pfile->source_date_epoch = source_date_epoch; 
+  pfile->source_date_epoch = (time_t) -2;
 }
 
 /* Sanity-checks are dependent on command-line options, so it is
diff --git a/libcpp/internal.h b/libcpp/internal.h
index e3eb26b..cea32ec 100644
--- a/libcpp/internal.h
+++ b/libcpp/internal.h
@@ -503,7 +503,8 @@ struct cpp_reader
   const unsigned char *time;
 
   /* Externally set timestamp to replace current date and time useful for
-     reproducibility.  */
+     reproducibility.  It should be initialized to -2 (not yet set) and
+     set to -1 to disable it or to a non-negative value to enable it.  */
   time_t source_date_epoch;
 
   /* EOF token, and a token forcing paste avoidance.  */
diff --git a/libcpp/macro.c b/libcpp/macro.c
index c2a8376..55e53bf 100644
--- a/libcpp/macro.c
+++ b/libcpp/macro.c
@@ -358,9 +358,13 @@ _cpp_builtin_macro_text (cpp_reader *pfile, cpp_hashnode *node,
 	  struct tm *tb = NULL;
 
 	  /* Set a reproducible timestamp for __DATE__ and __TIME__ macro
-	     usage if SOURCE_DATE_EPOCH is defined.  */
-	  if (pfile->source_date_epoch != (time_t) -1)
-	     tb = gmtime (&pfile->source_date_epoch);
+	     if SOURCE_DATE_EPOCH is defined.  */
+	  if (pfile->source_date_epoch == (time_t) -2
+	      && pfile->cb.get_source_date_epoch != NULL)
+	      pfile->source_date_epoch = pfile->cb.get_source_date_epoch(pfile);
+
+	  if (pfile->source_date_epoch >= (time_t) 0)
+	    tb = gmtime (&pfile->source_date_epoch);
 	  else
 	    {
 	      /* (time_t) -1 is a legitimate value for "number of seconds
