diff --git a/betterproto/casing.py b/betterproto/casing.py
index 01e10bb..60ece6a 100644
--- a/betterproto/casing.py
+++ b/betterproto/casing.py
@@ -53,30 +53,65 @@ def safe_snake_case(value: str) -> str:
     return value
 
 
-def snake_case(value: str):
+def snake_case(value: str, strict: bool = True):
     """
     Join words with an underscore into lowercase and remove symbols.
+    @param value: value to convert
+    @param strict: force single underscores
     """
+
+    def substitute_word(symbols, word, is_start):
+        if not word:
+            return ""
+        if strict:
+            delimiter_count = 0 if is_start else 1  # Single underscore if strict.
+        elif is_start:
+            delimiter_count = len(symbols)
+        elif word.isupper() or word.islower():
+            delimiter_count = max(1, len(symbols))  # Preserve all delimiters if not strict.
+        else:
+            delimiter_count = len(symbols) + 1  # Extra underscore for leading capital.
+
+        return ("_" * delimiter_count) + word.lower()
+
     snake = re.sub(
-        f"{SYMBOLS}({WORD_UPPER}|{WORD})", lambda groups: "_" + groups[1].lower(), value
+        f"(^)?({SYMBOLS})({WORD_UPPER}|{WORD})",
+        lambda groups: substitute_word(groups[2], groups[3], groups[1] is not None),
+        value,
     )
-    return snake.strip("_")
+    return snake
 
 
-def pascal_case(value: str):
+def pascal_case(value: str, strict: bool = True):
     """
     Capitalize each word and remove symbols.
+    @param value: value to convert
+    @param strict: output only alphanumeric characters
     """
+
+    def substitute_word(symbols, word):
+        if strict:
+            return word.capitalize()  # Remove all delimiters
+
+        if word.islower():
+            delimiter_length = len(symbols[:-1])  # Lose one delimiter
+        else:
+            delimiter_length = len(symbols)  # Preserve all delimiters
+
+        return ("_" * delimiter_length) + word.capitalize()
+
     return re.sub(
-        f"{SYMBOLS}({WORD_UPPER}|{WORD})", lambda groups: groups[1].capitalize(), value
+        f"({SYMBOLS})({WORD_UPPER}|{WORD})",
+        lambda groups: substitute_word(groups[1], groups[2]),
+        value,
     )
 
 
-def camel_case(value: str):
+def camel_case(value: str, strict: bool = True):
     """
     Capitalize all words except first and remove symbols.
     """
-    return lowercase_first(pascal_case(value))
+    return lowercase_first(pascal_case(value, strict=strict))
 
 
 def lowercase_first(value: str):
diff --git a/betterproto/tests/test_casing.py b/betterproto/tests/test_casing.py
index ac18309..ec60483 100644
--- a/betterproto/tests/test_casing.py
+++ b/betterproto/tests/test_casing.py
@@ -29,7 +29,7 @@ from betterproto.casing import camel_case, pascal_case, snake_case
     ],
 )
 def test_pascal_case(value, expected):
-    actual = pascal_case(value)
+    actual = pascal_case(value, strict=True)
     assert actual == expected, f"{value} => {expected} (actual: {actual})"
 
 
@@ -56,8 +56,22 @@ def test_pascal_case(value, expected):
         ("1foobar", "1Foobar"),
     ],
 )
-def test_camel_case(value, expected):
-    actual = camel_case(value)
+def test_camel_case_strict(value, expected):
+    actual = camel_case(value, strict=True)
+    assert actual == expected, f"{value} => {expected} (actual: {actual})"
+
+
+@pytest.mark.parametrize(
+    ["value", "expected"],
+    [
+        ("foo_bar", "fooBar"),
+        ("FooBar", "fooBar"),
+        ("foo__bar", "foo_Bar"),
+        ("foo__Bar", "foo__Bar"),
+    ],
+)
+def test_camel_case_not_strict(value, expected):
+    actual = camel_case(value, strict=False)
     assert actual == expected, f"{value} => {expected} (actual: {actual})"
 
 
@@ -71,6 +85,7 @@ def test_camel_case(value, expected):
         ("FooBar", "foo_bar"),
         ("foo.bar", "foo_bar"),
         ("foo_bar", "foo_bar"),
+        ("foo_Bar", "foo_bar"),
         ("FOOBAR", "foobar"),
         ("FOOBar", "foo_bar"),
         ("UInt32", "u_int32"),
@@ -85,8 +100,26 @@ def test_camel_case(value, expected):
         ("foo~bar", "foo_bar"),
         ("foo:bar", "foo_bar"),
         ("1foobar", "1_foobar"),
+        ("GetUInt64", "get_u_int64"),
     ],
 )
-def test_snake_case(value, expected):
+def test_snake_case_strict(value, expected):
     actual = snake_case(value)
     assert actual == expected, f"{value} => {expected} (actual: {actual})"
+
+
+@pytest.mark.parametrize(
+    ["value", "expected"],
+    [
+        ("fooBar", "foo_bar"),
+        ("FooBar", "foo_bar"),
+        ("foo_Bar", "foo__bar"),
+        ("foo__bar", "foo__bar"),
+        ("FOOBar", "foo_bar"),
+        ("__foo", "__foo"),
+        ("GetUInt64", "get_u_int64"),
+    ],
+)
+def test_snake_case_not_strict(value, expected):
+    actual = snake_case(value, strict=False)
+    assert actual == expected, f"{value} => {expected} (actual: {actual})"