diff --git a/gcc/ada/ChangeLog b/gcc/ada/ChangeLog
index 92ec7513bd58..ba9599e2980a 100644
--- a/gcc/ada/ChangeLog
+++ b/gcc/ada/ChangeLog
@@ -1,3 +1,8 @@
+2018-07-31  Arnaud Charlet  <charlet@adacore.com>
+
+	* gnatlink.adb: Fix potential Constraint_Error if
+	Library_Version is too long.
+
 2018-07-31  Arnaud Charlet  <charlet@adacore.com>
 
 	* sem_elab.adb: Remove duplicate condition detected by CodePeer.
diff --git a/gcc/ada/gnatlink.adb b/gcc/ada/gnatlink.adb
index f712a7abb6c5..16981b88d5c0 100644
--- a/gcc/ada/gnatlink.adb
+++ b/gcc/ada/gnatlink.adb
@@ -1102,8 +1102,10 @@ procedure Gnatlink is
                   --  We will be looking for the static version of the library
                   --  as it is in the same directory as the shared version.
 
-                  if Next_Line (Nlast - Library_Version'Length + 1 .. Nlast) =
-                       Library_Version
+                  if Nlast >= Library_Version'Length
+                    and then Next_Line
+                      (Nlast - Library_Version'Length + 1 .. Nlast)
+                        = Library_Version
                   then
                      --  Set Last to point to last character before the
                      --  library version.