diff --git a/src/testdir/test86.in b/src/testdir/test86.in
index 395ba96..93eb400 100644
--- a/src/testdir/test86.in
+++ b/src/testdir/test86.in
@@ -176,28 +176,62 @@
 :else
 :   $put ='[0.0, 0.0]'
 :endif
+:let messages=[]
+:py <<EOF
+d=vim.bindeval('{}')
+m=vim.bindeval('messages')
+try:
+    d['abc']
+except Exception as e:
+    m.extend([e.__class__.__name__])
+
+try:
+    d['abc']="\0"
+except Exception as e:
+    m.extend([e.__class__.__name__])
+
+try:
+    d['abc']=vim
+except Exception as e:
+    m.extend([e.__class__.__name__])
+
+try:
+    d['']=1
+except Exception as e:
+    m.extend([e.__class__.__name__])
+
+try:
+    d['a\0b']=1
+except Exception as e:
+    m.extend([e.__class__.__name__])
+
+try:
+    d[b'a\0b']=1
+except Exception as e:
+    m.extend([e.__class__.__name__])
+EOF
+:$put =messages
 :"
 :" pyeval()
 :let l=pyeval('range(3)')
 :$put =string(l)
 :let d=pyeval('{"a": "b", "c": 1, "d": ["e"]}')
 :$put =sort(items(d))
-:try
-:   let undef=pyeval('undefined_name')
-:catch
-:   $put =v:exception[:13]
-:endtry
-:try
-:   let vim=pyeval('vim')
-:catch
-:   $put =v:exception[:13]
-:endtry
 :if has('float')
 :   let f=pyeval('0.0')
 :   $put =string(f)
 :else
 :   $put ='0.0'
 :endif
+:" Invalid values:
+:for e in ['"\0"', '{"\0": 1}', 'undefined_name', 'vim']
+:   try
+:      let v=pyeval(e)
+:   catch
+:      let toput=e.":\t".v:exception[:13]
+:      $put =toput
+:   endtry
+:endfor
 :endfun
 :"
 :call Test()
diff --git a/src/testdir/test86.ok b/src/testdir/test86.ok
index ebf9f88..94f36e9 100644
--- a/src/testdir/test86.ok
+++ b/src/testdir/test86.ok
@@ -38,10 +38,18 @@
 Vim(python):E725:
 Vim(python):E117:
 [0.0, 0.0]
+IndexError
+TypeError
+TypeError
+ValueError
+TypeError
+TypeError
 [0, 1, 2]
 ['a', 'b']
 ['c', 1]
 ['d', ['e']]
-Vim(let):E858:
-Vim(let):E859:
 0.0
+"\0":	Vim(let):E859:
+{"\0": 1}:	Vim(let):E859:
+undefined_name:	Vim(let):E858:
+vim:	Vim(let):E859:
diff --git a/src/testdir/test87.in b/src/testdir/test87.in
index 8e48605..312763c 100644
--- a/src/testdir/test87.in
+++ b/src/testdir/test87.in
@@ -176,28 +176,62 @@
 :else
 :   $put ='[0.0, 0.0]'
 :endif
+:let messages=[]
+:py3 <<EOF
+d=vim.bindeval('{}')
+m=vim.bindeval('messages')
+try:
+    d['abc']
+except Exception as e:
+    m.extend([e.__class__.__name__])
+
+try:
+    d['abc']="\0"
+except Exception as e:
+    m.extend([e.__class__.__name__])
+
+try:
+    d['abc']=vim
+except Exception as e:
+    m.extend([e.__class__.__name__])
+
+try:
+    d['']=1
+except Exception as e:
+    m.extend([e.__class__.__name__])
+
+try:
+    d['a\0b']=1
+except Exception as e:
+    m.extend([e.__class__.__name__])
+
+try:
+    d[b'a\0b']=1
+except Exception as e:
+    m.extend([e.__class__.__name__])
+EOF
+:$put =messages
 :"
 :" py3eval()
 :let l=py3eval('[0, 1, 2]')
 :$put =string(l)
 :let d=py3eval('{"a": "b", "c": 1, "d": ["e"]}')
 :$put =sort(items(d))
-:try
-:   let undef=py3eval('undefined_name')
-:catch
-:   $put =v:exception[:13]
-:endtry
-:try
-:   let vim=py3eval('vim')
-:catch
-:   $put =v:exception[:13]
-:endtry
 :if has('float')
 :   let f=py3eval('0.0')
 :   $put =string(f)
 :else
 :   $put ='0.0'
 :endif
+:" Invalid values:
+:for e in ['"\0"', '{"\0": 1}', 'undefined_name', 'vim']
+:   try
+:      let v=py3eval(e)
+:   catch
+:      let toput=e.":\t".v:exception[:13]
+:      $put =toput
+:   endtry
+:endfor
 :endfun
 :"
 :call Test()
diff --git a/src/testdir/test87.ok b/src/testdir/test87.ok
index bcc4872..4eab845 100644
--- a/src/testdir/test87.ok
+++ b/src/testdir/test87.ok
@@ -38,10 +38,18 @@
 Vim(py3):E725:
 Vim(py3):E117:
 [0.0, 0.0]
+IndexError
+TypeError
+TypeError
+ValueError
+TypeError
+TypeError
 [0, 1, 2]
 ['a', 'b']
 ['c', 1]
 ['d', ['e']]
-Vim(let):E860:
-Vim(let):E861:
 0.0
+"\0":	Vim(let):E861:
+{"\0": 1}:	Vim(let):E861:
+undefined_name:	Vim(let):E860:
+vim:	Vim(let):E861:
diff --git a/src/version.c b/src/version.c
index 62bc819..06afdf2 100644
--- a/src/version.c
+++ b/src/version.c
@@ -720,6 +720,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    659,
+/**/
     658,
 /**/
     657,