diff --git a/src/alloc.c b/src/alloc.c
index 2cee646256..89372c11b5 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -3632,6 +3632,32 @@ Its value is void, and its function definition and property list are nil.  */)
   return val;
 }
 
+static Lisp_Object default_gensym_prefix;
+
+DEFUN ("gensym", Fgensym, Sgensym, 0, 1, 0,
+       doc: /* Return a new uninterned symbol.
+The name is made by concatenating PREFIX with a counter value.
+PREFIX is a string and defaults to "g".
+There is no provision for resetting the counter. */)
+  (Lisp_Object prefix)
+{
+  static int gensym_counter = 0;
+
+  Lisp_Object suffix, name;
+  int len;
+  char buf[INT_STRLEN_BOUND (EMACS_INT)];
+
+  if (NILP (prefix))
+    prefix = default_gensym_prefix;
+  CHECK_STRING (prefix);
+
+  EMACS_INT count = gensym_counter++;
+  len = sprintf (buf, "%"pI"d", count);
+  suffix = make_string (buf, len);
+  name = concat2 (prefix, suffix);
+  return Fmake_symbol (name);
+}
+
 
 
 /***********************************************************************
@@ -7515,6 +7541,8 @@ The time is in seconds as a floating point value.  */);
   DEFVAR_INT ("gcs-done", gcs_done,
               doc: /* Accumulated number of garbage collections done.  */);
 
+  default_gensym_prefix = build_pure_c_string ("g");
+
   defsubr (&Scons);
   defsubr (&Slist);
   defsubr (&Svector);
@@ -7527,6 +7555,7 @@ The time is in seconds as a floating point value.  */);
   defsubr (&Smake_string);
   defsubr (&Smake_bool_vector);
   defsubr (&Smake_symbol);
+  defsubr (&Sgensym);
   defsubr (&Smake_marker);
   defsubr (&Smake_finalizer);
   defsubr (&Spurecopy);