diff --git a/src/testdir/Make_dos.mak b/src/testdir/Make_dos.mak
index 8956384..9d1dc4e 100644
--- a/src/testdir/Make_dos.mak
+++ b/src/testdir/Make_dos.mak
@@ -19,6 +19,9 @@
 
 .SUFFIXES: .in .out .res .vim
 
+# Add --gui-dialog-file to avoid getting stuck in a dialog.
+COMMON_ARGS = $(NO_INITS) --gui-dialog-file guidialog
+
 nongui:	nolog tinytests newtests report
 
 gui:	nolog tinytests newtests report
@@ -31,7 +34,7 @@
 	@rem without the +eval feature test_result.log is a copy of test.log
 	@if exist test.log ( copy /y test.log test_result.log > nul ) \
 		else ( echo No failures reported > test_result.log )
-	$(VIMPROG) -u NONE $(NO_INITS) -S summarize.vim messages
+	$(VIMPROG) -u NONE $(COMMON_ARGS) -S summarize.vim messages
 	@echo.
 	@echo Test results:
 	@cmd /c type test_result.log
@@ -70,6 +73,8 @@
 	-if exist messages del messages
 	-if exist benchmark.out del benchmark.out
 	-if exist opt_test.vim del opt_test.vim
+	-if exist guidialog del guidialog
+	-if exist guidialogfile del guidialogfile
 
 nolog:
 	-if exist test.log del test.log
@@ -84,7 +89,7 @@
 $(DOSTMP_INFILES): $(*B).in
 	if not exist $(DOSTMP)\NUL md $(DOSTMP)
 	if exist $@ del $@
-	$(VIMPROG) -u dos.vim $(NO_INITS) "+set ff=dos|f $@|wq" $(*B).in
+	$(VIMPROG) -u dos.vim $(COMMON_ARGS) "+set ff=dos|f $@|wq" $(*B).in
 
 # For each input file dostmp/test99.in run the tests.
 # This moves test99.in to test99.in.bak temporarily.
@@ -94,7 +99,7 @@
 	move $(*B).in $(*B).in.bak > nul
 	copy $(DOSTMP)\$(*B).in $(*B).in > nul
 	copy $(*B).ok test.ok > nul
-	$(VIMPROG) -u dos.vim $(NO_INITS) -s dotest.in $(*B).in
+	$(VIMPROG) -u dos.vim $(COMMON_ARGS) -s dotest.in $(*B).in
 	-@if exist test.out MOVE /y test.out $(DOSTMP)\$(*B).out > nul
 	-@if exist $(*B).in.bak move /y $(*B).in.bak $(*B).in > nul
 	-@if exist test.ok del test.ok
@@ -103,7 +108,7 @@
 	-@if exist XfakeHOME rd /s /q XfakeHOME
 	-@del X*
 	-@if exist viminfo del viminfo
-	$(VIMPROG) -u dos.vim $(NO_INITS) "+set ff=unix|f test.out|wq" \
+	$(VIMPROG) -u dos.vim $(COMMON_ARGS) "+set ff=unix|f test.out|wq" \
 		$(DOSTMP)\$(*B).out
 	@diff test.out $*.ok & if errorlevel 1 \
 		( move /y test.out $*.failed > nul \
@@ -123,12 +128,12 @@
 
 .vim.res:
 	@echo $(VIMPROG) > vimcmd
-	$(VIMPROG) -u NONE $(NO_INITS) -S runtest.vim $*.vim
+	$(VIMPROG) -u NONE $(COMMON_ARGS) -S runtest.vim $*.vim
 	@del vimcmd
 
 test_gui.res: test_gui.vim
 	@echo $(VIMPROG) > vimcmd
-	$(VIMPROG) -u NONE $(NO_INITS) -S runtest.vim $*.vim
+	$(VIMPROG) -u NONE $(COMMON_ARGS) -S runtest.vim $*.vim
 	@del vimcmd
 
 test_gui_init.res: test_gui_init.vim
@@ -142,6 +147,6 @@
 test_bench_regexp.res: test_bench_regexp.vim
 	-if exist benchmark.out del benchmark.out
 	@echo $(VIMPROG) > vimcmd
-	$(VIMPROG) -u NONE $(NO_INITS) -S runtest.vim $*.vim
+	$(VIMPROG) -u NONE $(COMMON_ARGS) -S runtest.vim $*.vim
 	@del vimcmd
 	@IF EXIST benchmark.out ( type benchmark.out )
diff --git a/src/testdir/Make_ming.mak b/src/testdir/Make_ming.mak
index 5e17963..0638ade 100644
--- a/src/testdir/Make_ming.mak
+++ b/src/testdir/Make_ming.mak
@@ -31,6 +31,9 @@
 
 .SUFFIXES: .in .out .res .vim
 
+# Add --gui-dialog-file to avoid getting stuck in a dialog.
+COMMON_ARGS = $(NO_INITS) --gui-dialog-file guidialog
+
 nongui:	nolog tinytests newtests report
 
 gui:	nolog tinytests newtests report
@@ -43,7 +46,7 @@
 	@rem without the +eval feature test_result.log is a copy of test.log
 	@if exist test.log ( copy /y test.log test_result.log > nul ) \
 		else ( echo No failures reported > test_result.log )
-	$(VIMPROG) -u NONE $(NO_INITS) -S summarize.vim messages
+	$(VIMPROG) -u NONE $(COMMON_ARGS) -S summarize.vim messages
 	@echo.
 	@echo Test results:
 	@cmd /c type test_result.log
@@ -82,6 +85,8 @@
 	-@if exist messages $(DEL) messages
 	-@if exist benchmark.out del benchmark.out
 	-@if exist opt_test.vim $(DEL) opt_test.vim
+	-@if exist guidialog $(DEL) guidialog
+	-@if exist guidialogfile $(DEL) guidialogfile
 
 nolog:
 	-@if exist test.log $(DEL) test.log
@@ -96,7 +101,7 @@
 $(DOSTMP)/%.in : %.in
 	if not exist $(DOSTMP)\nul mkdir $(DOSTMP)
 	if exist $(DOSTMP)\$< $(DEL) $(DOSTMP)\$<
-	$(VIMPROG) -u dos.vim $(NO_INITS) "+set ff=dos|f $@|wq" $<
+	$(VIMPROG) -u dos.vim $(COMMON_ARGS) "+set ff=dos|f $@|wq" $<
 
 # For each input file dostmp/test99.in run the tests.
 # This moves test99.in to test99.in.bak temporarily.
@@ -106,7 +111,7 @@
 	$(MV) $(notdir $<) $(notdir $<).bak > NUL
 	$(CP) $(DOSTMP)\$(notdir $<) $(notdir $<) > NUL
 	$(CP) $(basename $@).ok test.ok > NUL
-	$(VIMPROG) -u dos.vim $(NO_INITS) -s dotest.in $(notdir $<)
+	$(VIMPROG) -u dos.vim $(COMMON_ARGS) -s dotest.in $(notdir $<)
 	-@if exist test.out $(MV) test.out $(DOSTMP)\$@ > NUL
 	-@if exist $(notdir $<).bak $(MV) $(notdir $<).bak $(notdir $<) > NUL
 	-@if exist test.ok $(DEL) test.ok
@@ -115,7 +120,7 @@
 	-@if exist XfakeHOME $(DELDIR) XfakeHOME
 	-@del X*
 	-@if exist viminfo del viminfo
-	$(VIMPROG) -u dos.vim $(NO_INITS) "+set ff=unix|f test.out|wq" \
+	$(VIMPROG) -u dos.vim $(COMMON_ARGS) "+set ff=unix|f test.out|wq" \
 		$(DOSTMP)\$@
 	@diff test.out $(basename $@).ok & if errorlevel 1 \
 		( $(MV) test.out $(basename $@).failed > NUL \
@@ -135,12 +140,12 @@
 
 .vim.res:
 	@echo $(VIMPROG) > vimcmd
-	$(VIMPROG) -u NONE $(NO_INITS) -S runtest.vim $*.vim
+	$(VIMPROG) -u NONE $(COMMON_ARGS) -S runtest.vim $*.vim
 	@$(DEL) vimcmd
 
 test_gui.res: test_gui.vim
 	@echo $(VIMPROG) > vimcmd
-	$(VIMPROG) -u NONE $(NO_INITS) -S runtest.vim $<
+	$(VIMPROG) -u NONE $(COMMON_ARGS) -S runtest.vim $<
 	@$(DEL) vimcmd
 
 test_gui_init.res: test_gui_init.vim
@@ -154,6 +159,6 @@
 test_bench_regexp.res: test_bench_regexp.vim
 	-$(DEL) benchmark.out
 	@echo $(VIMPROG) > vimcmd
-	$(VIMPROG) -u NONE $(NO_INITS) -S runtest.vim $*.vim
+	$(VIMPROG) -u NONE $(COMMON_ARGS) -S runtest.vim $*.vim
 	@$(DEL) vimcmd
 	$(CAT) benchmark.out
diff --git a/src/testdir/Makefile b/src/testdir/Makefile
index c782da9..adec1f1 100644
--- a/src/testdir/Makefile
+++ b/src/testdir/Makefile
@@ -89,6 +89,7 @@
 	-rm -rf $(RM_ON_RUN) $(RM_ON_START)
 	-rm -f valgrind.*
 	-rm -f asan.*
+	-rm -f guidialog guidialogfile
 
 # Delete the files produced by benchmarking, so they can run again.
 benchmarkclean:
@@ -127,7 +128,8 @@
 # New style of tests uses Vim script with assert calls.  These are easier
 # to write and a lot easier to read and debug.
 # Limitation: Only works with the +eval feature.
-RUN_VIMTEST = VIMRUNTIME=$(SCRIPTSOURCE) $(VALGRIND) $(VIMPROG) -f $(GUI_FLAG) -u unix.vim
+# Add --gui-dialog-file to avoid getting stuck in a dialog.
+RUN_VIMTEST = VIMRUNTIME=$(SCRIPTSOURCE) $(VALGRIND) $(VIMPROG) -f $(GUI_FLAG) -u unix.vim --gui-dialog-file guidialog
 
 newtests: newtestssilent
 	@/bin/sh -c "if test -f messages; then cat messages; fi"
diff --git a/src/testdir/runtest.vim b/src/testdir/runtest.vim
index 766f983..a4c238e 100644
--- a/src/testdir/runtest.vim
+++ b/src/testdir/runtest.vim
@@ -245,6 +245,12 @@
     call popup_clear(1)
   endif
 
+  if filereadable('guidialogfile')
+    call add(v:errors, "Unexpected dialog:")
+    call add(v:errors, readfile('guidialogfile').join('\n'))
+    call delete('guidialogfile')
+  endif
+
   " Close any extra tab pages and windows and make the current one not modified.
   while tabpagenr('$') > 1
     let winid = win_getid()
diff --git a/src/testdir/shared.vim b/src/testdir/shared.vim
index e442a59..60636fd 100644
--- a/src/testdir/shared.vim
+++ b/src/testdir/shared.vim
@@ -276,6 +276,7 @@
     let cmd = cmd . ' -u ' . name
   endif
   let cmd .= ' --not-a-term'
+  let cmd .= ' --gui-dialog-file guidialogfile'
   let cmd = substitute(cmd, 'VIMRUNTIME=\S\+', '', '')
 
   " If using valgrind, make sure every run uses a different log file.