diff --git a/flang/runtime/terminator.h b/flang/runtime/terminator.h
--- a/flang/runtime/terminator.h
+++ b/flang/runtime/terminator.h
@@ -34,7 +34,8 @@
       const char *predicate, const char *file, int line) const;
 
   // For test harnessing - overrides CrashArgs().
-  static void RegisterCrashHandler(void (*)(const char *, va_list &));
+  static void RegisterCrashHandler(void (*)(const char *sourceFile,
+      int sourceLine, const char *message, va_list &ap));
 
 private:
   const char *sourceFileName_{nullptr};
diff --git a/flang/runtime/terminator.cpp b/flang/runtime/terminator.cpp
--- a/flang/runtime/terminator.cpp
+++ b/flang/runtime/terminator.cpp
@@ -18,17 +18,18 @@
   CrashArgs(message, ap);
 }
 
-static void (*crashHandler)(const char *, va_list &){nullptr};
+static void (*crashHandler)(const char *, int, const char *, va_list &){
+    nullptr};
 
 void Terminator::RegisterCrashHandler(
-    void (*handler)(const char *, va_list &)) {
+    void (*handler)(const char *, int, const char *, va_list &)) {
   crashHandler = handler;
 }
 
 [[noreturn]] void Terminator::CrashArgs(
     const char *message, va_list &ap) const {
   if (crashHandler) {
-    crashHandler(message, ap);
+    crashHandler(sourceFileName_, sourceLine_, message, ap);
   }
   std::fputs("\nfatal Fortran runtime error", stderr);
   if (sourceFileName_) {
diff --git a/flang/unittests/Runtime/CMakeLists.txt b/flang/unittests/Runtime/CMakeLists.txt
--- a/flang/unittests/Runtime/CMakeLists.txt
+++ b/flang/unittests/Runtime/CMakeLists.txt
@@ -41,6 +41,18 @@
   LLVMSupport
 )
 
+add_executable(external-io
+  external-io.cpp
+)
+
+target_link_libraries(external-io
+  RuntimeTesting
+  FortranRuntime
+  LLVMSupport
+)
+
+add_test(NAME ExternalIO COMMAND external-io)
+
 add_executable(list-input-test
   list-input.cpp
 )
diff --git a/flang/unittests/Runtime/external-hello.cpp b/flang/unittests/Runtime/external-hello.cpp
--- a/flang/unittests/Runtime/external-hello.cpp
+++ b/flang/unittests/Runtime/external-hello.cpp
@@ -5,9 +5,8 @@
 
 using namespace Fortran::runtime::io;
 
-int main(int argc, const char *argv[], const char *envp[]) {
-  RTNAME(ProgramStart)(argc, argv, envp);
-  auto *io{IONAME(BeginExternalListOutput)()};
+void output1() {
+  auto io{IONAME(BeginExternalListOutput)()};
   const char str[]{"Hello, world!"};
   IONAME(OutputAscii)(io, str, std::strlen(str));
   IONAME(OutputInteger64)(io, 678);
@@ -21,6 +20,31 @@
   IONAME(OutputLogical)(io, false);
   IONAME(OutputLogical)(io, true);
   IONAME(EndIoStatement)(io);
+}
+
+void input1() {
+  auto io{IONAME(BeginExternalListOutput)()};
+  const char prompt[]{"Enter an integer value:"};
+  IONAME(OutputAscii)(io, prompt, std::strlen(prompt));
+  IONAME(EndIoStatement)(io);
+
+  io = IONAME(BeginExternalListInput)();
+  std::int64_t n{-666};
+  IONAME(InputInteger)(io, n);
+  IONAME(EndIoStatement)(io);
+
+  io = IONAME(BeginExternalListOutput)();
+  const char str[]{"Result:"};
+  IONAME(OutputAscii)(io, str, std::strlen(str));
+  IONAME(OutputInteger64)(io, n);
+  IONAME(EndIoStatement)(io);
+}
+
+int main(int argc, const char *argv[], const char *envp[]) {
+  RTNAME(ProgramStart)(argc, argv, envp);
+  output1();
+  input1();
+  RTNAME(PauseStatement)();
   RTNAME(ProgramEndStatement)();
   return 0;
 }
diff --git a/flang/unittests/Runtime/testing.h b/flang/unittests/Runtime/testing.h
--- a/flang/unittests/Runtime/testing.h
+++ b/flang/unittests/Runtime/testing.h
@@ -12,6 +12,7 @@
 llvm::raw_ostream &Fail();
 int EndTests();
 
+// Defines a CHARACTER object with padding when needed
 void SetCharacter(char *, std::size_t, const char *);
 
 #endif // FORTRAN_TEST_RUNTIME_TESTING_H_
diff --git a/flang/unittests/Runtime/testing.cpp b/flang/unittests/Runtime/testing.cpp
--- a/flang/unittests/Runtime/testing.cpp
+++ b/flang/unittests/Runtime/testing.cpp
@@ -9,10 +9,13 @@
 static int failures{0};
 
 // Override the Fortran runtime's Crash() for testing purposes
-[[noreturn]] static void CatchCrash(const char *message, va_list &ap) {
+[[noreturn]] static void CatchCrash(
+    const char *sourceFile, int sourceLine, const char *message, va_list &ap) {
   char buffer[1000];
   std::vsnprintf(buffer, sizeof buffer, message, ap);
   va_end(ap);
+  llvm::errs() << (sourceFile ? sourceFile : "unknown source file") << '('
+               << sourceLine << "): CRASH: " << buffer << '\n';
   throw std::string{buffer};
 }