diff --git a/lexer.go b/lexer.go
index 001049d..41b8af7 100644
--- a/lexer.go
+++ b/lexer.go
@@ -138,7 +138,7 @@
 			return l.lexRvalue
 		}
 
-		if isKeyChar(next) {
+		if isKeyStartChar(next) {
 			return l.lexKey
 		}
 
@@ -250,7 +250,10 @@
 
 func (l *tomlLexer) lexKey() tomlLexStateFn {
 	l.ignore()
-	for isKeyChar(l.next()) {
+	for r := l.next(); isKeyChar(r); r = l.next() {
+		if (r == '#') {
+			return l.errorf("keys cannot contain # character")
+		}
 	}
 	l.backup()
 	l.emit(tokenKey)
diff --git a/lexer_test.go b/lexer_test.go
index 019a496..176abf8 100644
--- a/lexer_test.go
+++ b/lexer_test.go
@@ -118,19 +118,16 @@
 
 func TestKeyWithSharpAndEqual(t *testing.T) {
 	testFlow(t, "key#name = 5", []token{
-		token{Position{1, 1}, tokenKey, "key#name"},
-		token{Position{1, 10}, tokenEqual, "="},
-		token{Position{1, 12}, tokenInteger, "5"},
-		token{Position{1, 13}, tokenEOF, ""},
+		token{Position{1, 1}, tokenError, "keys cannot contain # character"},
 	})
 }
 
 func TestKeyWithSymbolsAndEqual(t *testing.T) {
-	testFlow(t, "~!@#$^&*()_+-`1234567890[]\\|/?><.,;:' = 5", []token{
-		token{Position{1, 1}, tokenKey, "~!@#$^&*()_+-`1234567890[]\\|/?><.,;:'"},
-		token{Position{1, 39}, tokenEqual, "="},
-		token{Position{1, 41}, tokenInteger, "5"},
-		token{Position{1, 42}, tokenEOF, ""},
+	testFlow(t, "~!@$^&*()_+-`1234567890[]\\|/?><.,;:' = 5", []token{
+		token{Position{1, 1}, tokenKey, "~!@$^&*()_+-`1234567890[]\\|/?><.,;:'"},
+		token{Position{1, 38}, tokenEqual, "="},
+		token{Position{1, 40}, tokenInteger, "5"},
+		token{Position{1, 41}, tokenEOF, ""},
 	})
 }
 
diff --git a/parser_test.go b/parser_test.go
index 238ca2f..136c795 100644
--- a/parser_test.go
+++ b/parser_test.go
@@ -54,9 +54,9 @@
 // NOTE: from the BurntSushi test suite
 // NOTE: this test is pure evil due to the embedded '.'
 func TestSpecialKV(t *testing.T) {
-	tree, err := Load("~!@#$^&*()_+-`1234567890[]\\|/?><.,;: = 1")
+	tree, err := Load("~!@$^&*()_+-`1234567890[]\\|/?><.,;: = 1")
 	assertTree(t, tree, err, map[string]interface{}{
-		"~!@#$^&*()_+-`1234567890[]\\|/?><.,;:": int64(1),
+		"~!@$^&*()_+-`1234567890[]\\|/?><.,;:": int64(1),
 	})
 }
 
diff --git a/token.go b/token.go
index 22ad37a..6c0bcc6 100644
--- a/token.go
+++ b/token.go
@@ -117,11 +117,16 @@
 }
 
 func isKeyChar(r rune) bool {
-	// "Keys start with the first non-whitespace character and end with the last
-	// non-whitespace character before the equals sign."
+	// Keys start with the first character that isn't whitespace or [ and end
+	// with the last non-whitespace character before the equals sign. Keys
+	// cannot contain a # character."
 	return !(isSpace(r) || r == '\r' || r == '\n' || r == eof || r == '=')
 }
 
+func isKeyStartChar(r rune) bool {
+	return !(isSpace(r) || r == '\r' || r == '\n' || r == eof || r == '[')
+}
+
 func isDigit(r rune) bool {
 	return unicode.IsNumber(r)
 }