diff --git a/gcc/ada/ChangeLog b/gcc/ada/ChangeLog
index 84dd18b7767..e032be37062 100644
--- a/gcc/ada/ChangeLog
+++ b/gcc/ada/ChangeLog
@@ -1,3 +1,9 @@
+2018-06-11  Bob Duff  <duff@adacore.com>
+
+	* libgnat/a-ciorma.adb, libgnat/a-ciormu.adb, libgnat/a-ciorse.adb,
+	libgnat/a-coorma.adb, libgnat/a-coormu.adb, libgnat/a-coorse.adb:
+	(Element): Add code to detect dangling cursors in some cases.
+
 2018-06-11  Yannick Moy  <moy@adacore.com>
 
 	* sem_ch6.adb (Build_Subprogram_Declaration): Mark parameters as coming
diff --git a/gcc/ada/libgnat/a-ciorma.adb b/gcc/ada/libgnat/a-ciorma.adb
index a981f7219f7..000851a8cac 100644
--- a/gcc/ada/libgnat/a-ciorma.adb
+++ b/gcc/ada/libgnat/a-ciorma.adb
@@ -541,6 +541,13 @@ package body Ada.Containers.Indefinite_Ordered_Maps is
            "Position cursor of function Element is bad";
       end if;
 
+      if Checks and then
+        (Left (Position.Node) = Position.Node
+           or else Right (Position.Node) = Position.Node)
+      then
+         raise Program_Error with "dangling cursor";
+      end if;
+
       pragma Assert (Vet (Position.Container.Tree, Position.Node),
                      "Position cursor of function Element is bad");
 
diff --git a/gcc/ada/libgnat/a-ciormu.adb b/gcc/ada/libgnat/a-ciormu.adb
index 2420788cc4f..5c3e9f75bb2 100644
--- a/gcc/ada/libgnat/a-ciormu.adb
+++ b/gcc/ada/libgnat/a-ciormu.adb
@@ -545,6 +545,13 @@ package body Ada.Containers.Indefinite_Ordered_Multisets is
          raise Program_Error with "Position cursor is bad";
       end if;
 
+      if Checks and then
+        (Left (Position.Node) = Position.Node
+           or else Right (Position.Node) = Position.Node)
+      then
+         raise Program_Error with "dangling cursor";
+      end if;
+
       pragma Assert (Vet (Position.Container.Tree, Position.Node),
                      "bad cursor in Element");
 
diff --git a/gcc/ada/libgnat/a-ciorse.adb b/gcc/ada/libgnat/a-ciorse.adb
index e6565136aa1..7394a4aedc5 100644
--- a/gcc/ada/libgnat/a-ciorse.adb
+++ b/gcc/ada/libgnat/a-ciorse.adb
@@ -534,6 +534,13 @@ package body Ada.Containers.Indefinite_Ordered_Sets is
          raise Program_Error with "Position cursor is bad";
       end if;
 
+      if Checks and then
+        (Left (Position.Node) = Position.Node
+           or else Right (Position.Node) = Position.Node)
+      then
+         raise Program_Error with "dangling cursor";
+      end if;
+
       pragma Assert (Vet (Position.Container.Tree, Position.Node),
                      "bad cursor in Element");
 
diff --git a/gcc/ada/libgnat/a-coorma.adb b/gcc/ada/libgnat/a-coorma.adb
index 05eea5bc494..5fd3ec68a50 100644
--- a/gcc/ada/libgnat/a-coorma.adb
+++ b/gcc/ada/libgnat/a-coorma.adb
@@ -481,6 +481,13 @@ package body Ada.Containers.Ordered_Maps is
            "Position cursor of function Element equals No_Element";
       end if;
 
+      if Checks and then
+        (Left (Position.Node) = Position.Node
+           or else Right (Position.Node) = Position.Node)
+      then
+         raise Program_Error with "dangling cursor";
+      end if;
+
       pragma Assert (Vet (Position.Container.Tree, Position.Node),
                      "Position cursor of function Element is bad");
 
diff --git a/gcc/ada/libgnat/a-coormu.adb b/gcc/ada/libgnat/a-coormu.adb
index 0fc1063bd40..c114cf9f48a 100644
--- a/gcc/ada/libgnat/a-coormu.adb
+++ b/gcc/ada/libgnat/a-coormu.adb
@@ -502,6 +502,13 @@ package body Ada.Containers.Ordered_Multisets is
          raise Constraint_Error with "Position cursor equals No_Element";
       end if;
 
+      if Checks and then
+        (Left (Position.Node) = Position.Node
+           or else Right (Position.Node) = Position.Node)
+      then
+         raise Program_Error with "dangling cursor";
+      end if;
+
       pragma Assert (Vet (Position.Container.Tree, Position.Node),
                      "bad cursor in Element");
 
diff --git a/gcc/ada/libgnat/a-coorse.adb b/gcc/ada/libgnat/a-coorse.adb
index 606938ec3c0..1f96d39499a 100644
--- a/gcc/ada/libgnat/a-coorse.adb
+++ b/gcc/ada/libgnat/a-coorse.adb
@@ -480,6 +480,13 @@ package body Ada.Containers.Ordered_Sets is
          raise Constraint_Error with "Position cursor equals No_Element";
       end if;
 
+      if Checks and then
+        (Left (Position.Node) = Position.Node
+           or else Right (Position.Node) = Position.Node)
+      then
+         raise Program_Error with "dangling cursor";
+      end if;
+
       pragma Assert (Vet (Position.Container.Tree, Position.Node),
                      "bad cursor in Element");