diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 13580de7525..75ff1342713 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,12 @@
+2019-02-20  David Malcolm  <dmalcolm@redhat.com>
+
+	PR c/89410
+	* diagnostic-show-locus.c (layout::calculate_line_spans): Use
+	linenum_arith_t when determining if two adjacent line spans are
+	close enough to merge.
+	(diagnostic_show_locus): Use linenum_arith_t when iterating over
+	lines within each line_span.
+
 2019-02-20 Andre Vieira  <andre.simoesdiasvieira@arm.com>
 
 	PR target/86487
diff --git a/gcc/diagnostic-show-locus.c b/gcc/diagnostic-show-locus.c
index ddc9421ce63..205ee56f409 100644
--- a/gcc/diagnostic-show-locus.c
+++ b/gcc/diagnostic-show-locus.c
@@ -1211,7 +1211,8 @@ layout::calculate_line_spans ()
       const line_span *next = &tmp_spans[i];
       gcc_assert (next->m_first_line >= current->m_first_line);
       const int merger_distance = m_show_line_numbers_p ? 1 : 0;
-      if (next->m_first_line <= current->m_last_line + 1 + merger_distance)
+      if ((linenum_arith_t)next->m_first_line
+	  <= (linenum_arith_t)current->m_last_line + 1 + merger_distance)
 	{
 	  /* We can merge them. */
 	  if (next->m_last_line > current->m_last_line)
@@ -2301,8 +2302,10 @@ diagnostic_show_locus (diagnostic_context * context,
 	      context->start_span (context, exploc);
 	    }
 	}
-      linenum_type last_line = line_span->get_last_line ();
-      for (linenum_type row = line_span->get_first_line ();
+      /* Iterate over the lines within this span (using linenum_arith_t to
+	 avoid overflow with 0xffffffff causing an infinite loop).  */
+      linenum_arith_t last_line = line_span->get_last_line ();
+      for (linenum_arith_t row = line_span->get_first_line ();
 	   row <= last_line; row++)
 	layout.print_line (row);
     }
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 7a407cdba20..9d344ba7c2d 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2019-02-20  David Malcolm  <dmalcolm@redhat.com>
+
+	PR c/89410
+	* gcc.dg/pr89410-1.c: New test.
+	* gcc.dg/pr89410-2.c: New test.
+
 2019-02-20  Pat Haugen  <pthaugen@us.ibm.com>
 
 	* lib/target-supports.exp (check_effective_target_vect_usad_char):
diff --git a/gcc/testsuite/gcc.dg/pr89410-1.c b/gcc/testsuite/gcc.dg/pr89410-1.c
new file mode 100644
index 00000000000..73dc6d4de3f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr89410-1.c
@@ -0,0 +1,9 @@
+/* { dg-options "" } */
+
+int main(void)
+{
+  /* This is 0xffffffff.  */
+#line 4294967295
+#warning msg
+  /* { dg-warning "msg" "" { target *-*-* } -1 } */
+}
diff --git a/gcc/testsuite/gcc.dg/pr89410-2.c b/gcc/testsuite/gcc.dg/pr89410-2.c
new file mode 100644
index 00000000000..76e781b09df
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr89410-2.c
@@ -0,0 +1,13 @@
+/* { dg-options "-fdiagnostics-show-caret" } */
+
+int main(void)
+{
+  /* This is 0x7fffffffffffffff, which truncates to 0xffffffff.  */
+#line 9223372036854775807 /* { dg-warning "line number out of range" } */
+#warning msg
+  /* { dg-begin-multiline-output "" }
+ #line 9223372036854775807
+       ^~~~~~~~~~~~~~~~~~~
+     { dg-end-multiline-output "" } */
+  /* { dg-warning "msg" "" { target *-*-* } -1 } */
+}
diff --git a/libcpp/ChangeLog b/libcpp/ChangeLog
index fa2fa7d97e8..355b4cb0f73 100644
--- a/libcpp/ChangeLog
+++ b/libcpp/ChangeLog
@@ -1,3 +1,9 @@
+2019-02-20  David Malcolm  <dmalcolm@redhat.com>
+
+	PR c/89410
+	* include/line-map.h (linenum_arith_t): New typedef.
+	(compare): Use it.
+
 2019-02-18  Martin Liska  <mliska@suse.cz>
 
 	PR c++/89383
diff --git a/libcpp/include/line-map.h b/libcpp/include/line-map.h
index a6eb87c2ec0..6c77c288855 100644
--- a/libcpp/include/line-map.h
+++ b/libcpp/include/line-map.h
@@ -49,13 +49,16 @@ along with this program; see the file COPYING3.  If not see
 /* The type of line numbers.  */
 typedef unsigned int linenum_type;
 
+/* A type for doing arithmetic on line numbers.  */
+typedef long long linenum_arith_t;
+
 /* A function for for use by qsort for comparing line numbers.  */
 
 inline int compare (linenum_type lhs, linenum_type rhs)
 {
-  /* Avoid truncation issues by using long long for the comparison,
+  /* Avoid truncation issues by using linenum_arith_t for the comparison,
      and only consider the sign of the result.  */
-  long long diff = (long long)lhs - (long long)rhs;
+  linenum_arith_t diff = (linenum_arith_t)lhs - (linenum_arith_t)rhs;
   if (diff)
     return diff > 0 ? 1 : -1;
   return 0;