diff --git a/flang/lib/Semantics/mod-file.cpp b/flang/lib/Semantics/mod-file.cpp
--- a/flang/lib/Semantics/mod-file.cpp
+++ b/flang/lib/Semantics/mod-file.cpp
@@ -1057,6 +1057,31 @@
       if (needed) {
         need_.push_back(symbol);
       }
+    } else if (symbol.has<SubprogramDetails>()) {
+      // An internal subprogram is needed if it is used as interface
+      // for a dummy or return value procedure.
+      bool needed{false};
+      const auto hasInterface{[&symbol](const Symbol *s) -> bool {
+        // Is 's' a procedure with interface 'symbol'?
+        if (s) {
+          if (const auto *sDetails{s->detailsIf<ProcEntityDetails>()}) {
+            const ProcInterface &sInterface{sDetails->interface()};
+            if (sInterface.symbol() == &symbol) {
+              return true;
+            }
+          }
+        }
+        return false;
+      }};
+      for (const Symbol *dummyArg : details.dummyArgs()) {
+        needed = needed || hasInterface(dummyArg);
+      }
+      if (details.isFunction()) {
+        needed = needed || hasInterface(&details.result());
+      }
+      if (needed && needSet_.insert(symbol).second) {
+        need_.push_back(symbol);
+      }
     }
   }
 }
diff --git a/flang/test/Semantics/modfile46.f90 b/flang/test/Semantics/modfile46.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/modfile46.f90
@@ -0,0 +1,55 @@
+! RUN: %python %S/test_modfile.py %s %flang_fc1
+! Ensure that interfaces, which are internal to procedures and are used to
+! define the interface of dummy or return value procedures, are included in
+! .mod files.
+module m
+  implicit none
+contains
+  function f(x)
+    real, intent(in) :: x
+    abstract interface
+       subroutine used_int(x, p)
+         implicit none
+         real, intent(out) :: x
+         interface
+            subroutine inner_int(x)
+              implicit none
+              real, intent(out) :: x
+            end subroutine inner_int
+         end interface
+         procedure(inner_int) :: p
+       end subroutine used_int
+
+       pure logical function unused_int(i)
+         implicit none
+         integer, intent(in) :: i
+       end function unused_int
+    end interface
+    procedure(used_int), pointer :: f
+
+    f => null()
+  contains
+    subroutine internal()
+    end subroutine internal
+  end function f
+end module m
+
+!Expect: m.mod
+!module m
+!contains
+!function f(x)
+!real(4),intent(in)::x
+!procedure(used_int),pointer::f
+!abstract interface
+!subroutine used_int(x,p)
+!real(4),intent(out)::x
+!procedure(inner_int)::p
+!interface
+!subroutine inner_int(x)
+!real(4),intent(out)::x
+!end
+!end interface
+!end
+!end interface
+!end
+!end