diff --git a/gas/ChangeLog b/gas/ChangeLog
index 22664296d8..1affd227fb 100644
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,3 +1,9 @@
+2015-04-29  Nick Clifton  <nickc@redhat.com>
+
+	* doc/as.texinfo (Set): Note that a symbol cannot be set multiple
+	times if the expression is not constant and the target uses linker
+	relaxation.
+
 2015-04-28  Renlin Li  <renlin.li@arm.com>
 
 	* config/tc-arm.c (arm_init_frag): Always emit mapping symbols.
diff --git a/gas/doc/as.texinfo b/gas/doc/as.texinfo
index ffdb97816d..d09e88cbac 100644
--- a/gas/doc/as.texinfo
+++ b/gas/doc/as.texinfo
@@ -6351,7 +6351,14 @@ changes @var{symbol}'s value and type to conform to
 @var{expression}.  If @var{symbol} was flagged as external, it remains
 flagged (@pxref{Symbol Attributes}).
 
-You may @code{.set} a symbol many times in the same assembly.
+You may @code{.set} a symbol many times in the same assembly provided that the
+values given to the symbol are constants.  Values that are based on expressions
+involving other symbols are allowed, but some targets may restrict this to only
+being done once per assembly.  This is because those targets do not set the
+addresses of symbols at assembly time, but rather delay the assignment until a
+final link is performed.  This allows the linker a chance to change the code in
+the files, changing the location of, and the relative distance between, various
+different symbols.
 
 If you @code{.set} a global symbol, the value stored in the object
 file is the last value stored into it.