diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 9731c99a6a..1a3cc6c30a 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2018-10-03  Tom Tromey  <tom@tromey.com>
+
+	* parse.c (prefixify_expression): Add assert.
+	(parse_exp_in_context_1): Throw exception if the expression is
+	empty.
+
 2018-10-03  Tom Tromey  <tom@tromey.com>
 
 	* dwarf2read.c (read_signed_leb128): Work in ULONGEST.
@@ -14219,7 +14225,7 @@
 
 	Update copyright year range in all GDB files.
 
-2018-01-01  Joel Brobecker  <brobecker@adacore.com>
+2018-01-01, 18  Joel Brobecker  <brobecker@adacore.com>
 
 	* copyright.py (BY_HAND): Remove gdb/testsuite/gdb.base/step-line.inp
 	and gdb/testsuite/gdb.base/step-line.c.
diff --git a/gdb/parse.c b/gdb/parse.c
index 163852cb84..8a128a74d7 100644
--- a/gdb/parse.c
+++ b/gdb/parse.c
@@ -792,6 +792,7 @@ copy_name (struct stoken token)
 int
 prefixify_expression (struct expression *expr)
 {
+  gdb_assert (expr->nelts > 0);
   int len = sizeof (struct expression) + EXP_ELEM_TO_BYTES (expr->nelts);
   struct expression *temp;
   int inpos = expr->nelts, outpos = 0;
@@ -1205,7 +1206,10 @@ parse_exp_in_context_1 (const char **stringptr, CORE_ADDR pc,
     }
   CATCH (except, RETURN_MASK_ALL)
     {
-      if (! parse_completion)
+      /* If parsing for completion, allow this to succeed; but if no
+	 expression elements have been written, then there's nothing
+	 to do, so fail.  */
+      if (! parse_completion || ps.expout_ptr == 0)
 	throw_exception (except);
     }
   END_CATCH