diff --git a/src/testdir/test_expr.vim b/src/testdir/test_expr.vim
index 1086534..754f856 100644
--- a/src/testdir/test_expr.vim
+++ b/src/testdir/test_expr.vim
@@ -42,6 +42,16 @@
   call assert_false(has('patch-9.9.1'))
 endfunc
 
+func Test_op_trinary()
+  call assert_equal('yes', 1 ? 'yes' : 'no')
+  call assert_equal('no', 0 ? 'yes' : 'no')
+  call assert_equal('no', 'x' ? 'yes' : 'no')
+  call assert_equal('yes', '1x' ? 'yes' : 'no')
+
+  call assert_fails('echo [1] ? "yes" : "no"', 'E745:')
+  call assert_fails('echo {} ? "yes" : "no"', 'E728:')
+endfunc
+
 func Test_op_falsy()
   call assert_equal(v:true, v:true ?? 456)
   call assert_equal(123, 123 ?? 456)
diff --git a/src/testdir/test_vim9_cmd.vim b/src/testdir/test_vim9_cmd.vim
index 82d5f32..599c287 100644
--- a/src/testdir/test_vim9_cmd.vim
+++ b/src/testdir/test_vim9_cmd.vim
@@ -68,6 +68,74 @@
   CheckScriptSuccess(lines)
 enddef
 
+def Test_condition_types()
+  var lines =<< trim END
+      if 'text'
+      endif
+  END
+  CheckDefAndScriptFailure(lines, 'E1030:', 1)
+
+  lines =<< trim END
+      if [1]
+      endif
+  END
+  CheckDefFailure(lines, 'E1012:', 1)
+  CheckScriptFailure(['vim9script'] + lines, 'E745:', 2)
+
+  lines =<< trim END
+      g:cond = 'text'
+      if g:cond
+      endif
+  END
+  CheckDefExecAndScriptFailure(lines, 'E1030:', 2)
+
+  lines =<< trim END
+      g:cond = 0
+      if g:cond
+      elseif 'text'
+      endif
+  END
+  CheckDefFailure(lines, 'E1012:', 3)
+  CheckScriptFailure(['vim9script'] + lines, 'E1030:', 4)
+
+  lines =<< trim END
+      if g:cond
+      elseif [1]
+      endif
+  END
+  CheckDefFailure(lines, 'E1012:', 2)
+  CheckScriptFailure(['vim9script'] + lines, 'E745:', 3)
+
+  lines =<< trim END
+      g:cond = 'text'
+      if 0
+      elseif g:cond
+      endif
+  END
+  CheckDefExecAndScriptFailure(lines, 'E1030:', 3)
+
+  lines =<< trim END
+      while 'text'
+      endwhile
+  END
+  CheckDefFailure(lines, 'E1012:', 1)
+  CheckScriptFailure(['vim9script'] + lines, 'E1030:', 2)
+
+  lines =<< trim END
+      while [1]
+      endwhile
+  END
+  CheckDefFailure(lines, 'E1012:', 1)
+  CheckScriptFailure(['vim9script'] + lines, 'E745:', 2)
+
+  lines =<< trim END
+      g:cond = 'text'
+      while g:cond
+      endwhile
+  END
+  CheckDefExecAndScriptFailure(lines, 'E1030:', 2)
+enddef
+
 def Test_if_linebreak()
   var lines =<< trim END
       vim9script
diff --git a/src/testdir/test_vim9_expr.vim b/src/testdir/test_vim9_expr.vim
index 5158e10..2cbb285 100644
--- a/src/testdir/test_vim9_expr.vim
+++ b/src/testdir/test_vim9_expr.vim
@@ -18,27 +18,27 @@
 			'one' :
 			'two')
   if has('float')
-    assert_equal('one', 0.1 ? 'one' : 'two')
+    assert_equal('one', !!0.1 ? 'one' : 'two')
   endif
-  assert_equal('one', 'x' ? 'one' : 'two')
-  assert_equal('one', 'x'
+  assert_equal('one', !!'x' ? 'one' : 'two')
+  assert_equal('one', !!'x'
   			? 'one'
 			: 'two')
-  assert_equal('one', 0z1234 ? 'one' : 'two')
-  assert_equal('one', [0] ? 'one' : 'two')
-  assert_equal('one', #{x: 0} ? 'one' : 'two')
+  assert_equal('one', !!0z1234 ? 'one' : 'two')
+  assert_equal('one', !![0] ? 'one' : 'two')
+  assert_equal('one', !!#{x: 0} ? 'one' : 'two')
   var name = 1
   assert_equal('one', name ? 'one' : 'two')
 
   assert_equal('two', false ? 'one' : 'two')
   assert_equal('two', 0 ? 'one' : 'two')
   if has('float')
-    assert_equal('two', 0.0 ? 'one' : 'two')
+    assert_equal('two', !!0.0 ? 'one' : 'two')
   endif
-  assert_equal('two', '' ? 'one' : 'two')
-  assert_equal('two', 0z ? 'one' : 'two')
-  assert_equal('two', [] ? 'one' : 'two')
-  assert_equal('two', {} ? 'one' : 'two')
+  assert_equal('two', !!'' ? 'one' : 'two')
+  assert_equal('two', !!0z ? 'one' : 'two')
+  assert_equal('two', !![] ? 'one' : 'two')
+  assert_equal('two', !!{} ? 'one' : 'two')
   name = 0
   assert_equal('two', name ? 'one' : 'two')
 
@@ -117,6 +117,24 @@
   END
   CheckScriptFailure(lines, 'E1004:', 2)
 
+  lines =<< trim END
+      vim9script
+      var name = 'x' ? 1 : 2
+  END
+  CheckScriptFailure(lines, 'E1030:', 2)
+
+  lines =<< trim END
+      vim9script
+      var name = [] ? 1 : 2
+  END
+  CheckScriptFailure(lines, 'E745:', 2)
+
+  lines =<< trim END
+      vim9script
+      var name = {} ? 1 : 2
+  END
+  CheckScriptFailure(lines, 'E728:', 2)
+
   # check after failure eval_flags is reset
   lines =<< trim END
       vim9script
@@ -152,6 +170,15 @@
   call CheckDefFailure(["var x = 1 ? 'one' :'two'"], msg, 1)
   call CheckDefFailure(["var x = 1 ? 'one':'two'"], msg, 1)
 
+  call CheckDefFailure(["var x = 'x' ? 'one' : 'two'"], 'E1030:', 1)
+  call CheckDefFailure(["var x = 0z1234 ? 'one' : 'two'"], 'E974:', 1)
+  call CheckDefExecFailure(["var x = [] ? 'one' : 'two'"], 'E745:', 1)
+  call CheckDefExecFailure(["var x = {} ? 'one' : 'two'"], 'E728:', 1)
+
+  if has('float')
+    call CheckDefFailure(["var x = 0.1 ? 'one' : 'two'"], 'E805:', 1)
+  endif
+
   " missing argument detected even when common type is used
   call CheckDefFailure([
 	\ 'var X = FuncOne',
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index 6dbabe3..7fc5223 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -543,7 +543,7 @@
   CheckDefFailure(['endtry'], 'E602:')
   CheckDefFailure(['while 1', 'endtry'], 'E170:')
   CheckDefFailure(['for i in range(5)', 'endtry'], 'E170:')
-  CheckDefFailure(['if 2', 'endtry'], 'E171:')
+  CheckDefFailure(['if 1', 'endtry'], 'E171:')
   CheckDefFailure(['try', 'echo 1', 'endtry'], 'E1032:')
 
   CheckDefFailure(['throw'], 'E1015:')
diff --git a/src/testdir/vim9.vim b/src/testdir/vim9.vim
index 2e4b03f..aeeb5a3 100644
--- a/src/testdir/vim9.vim
+++ b/src/testdir/vim9.vim
@@ -52,3 +52,10 @@
   CheckDefFailure(lines, error, lnum)
   CheckScriptFailure(['vim9script'] + lines, error, lnum + 1)
 enddef
+
+" Check that a command fails both when executed in a :def function and when
+" used in Vim9 script.
+def CheckDefExecAndScriptFailure(lines: list<string>, error: string, lnum = -3)
+  CheckDefExecFailure(lines, error, lnum)
+  CheckScriptFailure(['vim9script'] + lines, error, lnum + 1)
+enddef