diff --git a/lib/nokogiri/css/xpath_visitor.rb b/lib/nokogiri/css/xpath_visitor.rb
index ba63f3c4122..6d8ab67ce69 100644
--- a/lib/nokogiri/css/xpath_visitor.rb
+++ b/lib/nokogiri/css/xpath_visitor.rb
@@ -302,7 +302,7 @@ def nth(node, options = {})
       end
 
       def read_a_and_positive_b(values)
-        op = values[2]
+        op = values[2].strip
         if op == "+"
           a = values[0].to_i
           b = values[3].to_i
diff --git a/test/css/test_css_integration.rb b/test/css/test_css_integration.rb
index 9a0b47ce599..3d0e488f56e 100644
--- a/test/css/test_css_integration.rb
+++ b/test/css/test_css_integration.rb
@@ -194,6 +194,7 @@ def assert_result_rows(intarray, result, word = "row")
           assert_result_rows([5], subject.search("table//tr:nth-child(5)"))
           assert_result_rows([1, 3], subject.search("div/h1.c:nth-child(2)"), "header")
           assert_result_rows([3, 4], subject.search("div/i.b:nth-child(2n+1)"), "italic")
+          assert_result_rows([3, 4], subject.search("div/i.b:nth-child(2n + 1)"), "italic")
         end
 
         it "selects first_of_type" do
diff --git a/test/css/test_tokenizer.rb b/test/css/test_tokenizer.rb
index 878b708f4b1..5df220aba4c 100644
--- a/test/css/test_tokenizer.rb
+++ b/test/css/test_tokenizer.rb
@@ -226,6 +226,21 @@ def test_scan_nth
           @scanner,
         )
 
+        @scanner.scan("x:nth-child(5n + 3)")
+        assert_tokens(
+          [
+            [:IDENT, "x"],
+            [":", ":"],
+            [:FUNCTION, "nth-child("],
+            [:NUMBER, "5"],
+            [:IDENT, "n"],
+            [:PLUS, " + "],
+            [:NUMBER, "3"],
+            [:RPAREN, ")"],
+          ],
+          @scanner,
+        )
+
         @scanner.scan("x:nth-child(-1n+3)")
         assert_tokens(
           [
diff --git a/test/css/test_xpath_visitor.rb b/test/css/test_xpath_visitor.rb
index 4dbd2ff3219..5a5be68e13e 100644
--- a/test/css/test_xpath_visitor.rb
+++ b/test/css/test_xpath_visitor.rb
@@ -289,10 +289,12 @@ def assert_xpath(expecteds, asts)
       it ":nth(an+b)" do
         assert_xpath("//a[(position() mod 2)=0]", parser.parse("a:nth-of-type(2n)"))
         assert_xpath("//a[(position()>=1) and (((position()-1) mod 2)=0)]", parser.parse("a:nth-of-type(2n+1)"))
+        assert_xpath("//a[(position()>=1) and (((position()-1) mod 2)=0)]", parser.parse("a:nth-of-type(2n + 1)"))
         assert_xpath("//a[(position() mod 2)=0]", parser.parse("a:nth-of-type(even)"))
         assert_xpath("//a[(position()>=1) and (((position()-1) mod 2)=0)]", parser.parse("a:nth-of-type(odd)"))
         assert_xpath("//a[(position()>=3) and (((position()-3) mod 4)=0)]", parser.parse("a:nth-of-type(4n+3)"))
         assert_xpath("//a[position()<=3]", parser.parse("a:nth-of-type(-1n+3)"))
+        assert_xpath("//a[position()<=3]", parser.parse("a:nth-of-type(-1n +  3)"))
         assert_xpath("//a[position()<=3]", parser.parse("a:nth-of-type(-n+3)"))
         assert_xpath("//a[position()>=3]", parser.parse("a:nth-of-type(1n+3)"))
         assert_xpath("//a[position()>=3]", parser.parse("a:nth-of-type(n+3)"))