diff --git a/gcc/fortran/ChangeLog b/gcc/fortran/ChangeLog
index 17021990936f..bf721c7d43e8 100644
--- a/gcc/fortran/ChangeLog
+++ b/gcc/fortran/ChangeLog
@@ -1,3 +1,9 @@
+2019-09-13  Paul Thomas  <pault@gcc.gnu.org>
+
+	PR fortran/91717
+	* dependency.c (gfc_dep_resolver): Flag identical components
+	and exit with return value 1 if set and no array refs.
+
 2019-09-11  Steven G. Kargl  <kargl@gcc.gnu.org>
 
 	PR fortran/91553
diff --git a/gcc/fortran/dependency.c b/gcc/fortran/dependency.c
index da4a37c9e953..51148709766f 100644
--- a/gcc/fortran/dependency.c
+++ b/gcc/fortran/dependency.c
@@ -2096,6 +2096,7 @@ gfc_dep_resolver (gfc_ref *lref, gfc_ref *rref, gfc_reverse *reverse,
   int m;
   gfc_dependency fin_dep;
   gfc_dependency this_dep;
+  bool same_component = false;
 
   this_dep = GFC_DEP_ERROR;
   fin_dep = GFC_DEP_ERROR;
@@ -2115,6 +2116,8 @@ gfc_dep_resolver (gfc_ref *lref, gfc_ref *rref, gfc_reverse *reverse,
 	     components.  */
 	  if (lref->u.c.component != rref->u.c.component)
 	    return 0;
+
+	  same_component = true;
 	  break;
 
 	case REF_SUBSTRING:
@@ -2280,6 +2283,10 @@ gfc_dep_resolver (gfc_ref *lref, gfc_ref *rref, gfc_reverse *reverse,
   if (lref || rref)
     return 1;
 
+  /* This can result from concatenation of assumed length string components.  */
+  if (same_component && fin_dep == GFC_DEP_ERROR)
+    return 1;
+
   /* If we haven't seen any array refs then something went wrong.  */
   gcc_assert (fin_dep != GFC_DEP_ERROR);
 
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index cd805625ee61..ab1d7bc9312f 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2019-09-13  Paul Thomas  <pault@gcc.gnu.org>
+
+	PR fortran/91717
+	* gfortran.dg/dependency_55.f90 : New test.
+
 2019-09-12  Uroš Bizjak  <ubizjak@gmail.com>
 
 	PR tree-optimization/89386
diff --git a/gcc/testsuite/gfortran.dg/dependency_55.f90 b/gcc/testsuite/gfortran.dg/dependency_55.f90
new file mode 100644
index 000000000000..53898b3a34d7
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/dependency_55.f90
@@ -0,0 +1,18 @@
+! { dg-do run }
+!
+! Test the fix for PR91717 in which the concatenation operation ICEd.
+!
+! Contributed by Damian Rouson  <damian@sourceryinstitute.org>
+!
+  type core
+    character (len=:), allocatable :: msg
+  end type
+
+  type(core) :: my_core
+
+  my_core%msg = ""
+  my_core%msg = my_core%msg//"my message is: "
+  my_core%msg = my_core%msg//"Hello!"
+
+  if (my_core%msg .ne. "my message is: Hello!") stop 1
+end