diff --git a/CHANGES.md b/CHANGES.md
index d49a42cb..11db62d5 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -3,6 +3,7 @@
 ## python-markdown2 2.5.5 (not yet released)
 
 - [pull #639] Fix middle-word-em interfering with strongs (#637)
+- [pull #640] Fix code friendly extra stopping other syntax being processed (#638)
 
 
 ## python-markdown2 2.5.4
diff --git a/lib/markdown2.py b/lib/markdown2.py
index 9c2a4bf2..488b24cc 100755
--- a/lib/markdown2.py
+++ b/lib/markdown2.py
@@ -2960,20 +2960,28 @@ class CodeFriendly(ItalicAndBoldProcessor):
     '''
     name = 'code-friendly'
 
+    def __init__(self, md, options):
+        super().__init__(md, options)
+
+        # add a prefix to it so we don't interfere with escaped/hashed chars from other stages
+        self.hash_table[_hash_text(self.name + '_')] = '_'
+        self.hash_table[_hash_text(self.name + '__')] = '__'
+
     def sub(self, match: re.Match) -> str:
         syntax = match.group(1)
         text: str = match.string[match.start(): match.end()]
         if '_' in syntax:
-            # if using _this_ syntax, hash the whole thing so that it doesn't get processed
-            key = _hash_text(text)
-            self.hash_table[key] = text
-            return key
+            # if using _this_ syntax, hash it to avoid processing, but don't hash the contents incase of nested syntax
+            text = text.replace(syntax, _hash_text(self.name + syntax))
+            return text
         elif '_' in text:
-            # if the text within the bold/em markers contains '_' then hash those contents to protect them from em_re
-            text = text[len(syntax): -len(syntax)]
-            key = _hash_text(text)
-            self.hash_table[key] = text
-            return syntax + key + syntax
+            # if the text within the bold/em markers contains '_' then hash those chars to protect them from em_re
+            text = (
+                text[len(syntax): -len(syntax)]
+                .replace('__', _hash_text(self.name + '__'))
+                .replace('_', _hash_text(self.name + '_'))
+            )
+            return syntax + text + syntax
         # if no underscores are present, the text is fine and we can just leave it alone
         return super().sub(match)
 
diff --git a/test/tm-cases/code_friendly_issue638.html b/test/tm-cases/code_friendly_issue638.html
new file mode 100644
index 00000000..c28476e3
--- /dev/null
+++ b/test/tm-cases/code_friendly_issue638.html
@@ -0,0 +1 @@
+<p>a_b this should be <strong>bold</strong> c_d this is <strong>bold</strong></p>
diff --git a/test/tm-cases/code_friendly_issue638.opts b/test/tm-cases/code_friendly_issue638.opts
new file mode 100644
index 00000000..245e9828
--- /dev/null
+++ b/test/tm-cases/code_friendly_issue638.opts
@@ -0,0 +1 @@
+{"extras":["code-friendly"]}
\ No newline at end of file
diff --git a/test/tm-cases/code_friendly_issue638.text b/test/tm-cases/code_friendly_issue638.text
new file mode 100644
index 00000000..a015bf5c
--- /dev/null
+++ b/test/tm-cases/code_friendly_issue638.text
@@ -0,0 +1 @@
+a_b this should be **bold** c_d this is **bold**
\ No newline at end of file