diff --git a/requirements.txt b/requirements.txt
index 32b07ed..52f182a 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -5,4 +5,5 @@ pyyaml>=6.0
 twine>=3.8
 build>=0.7
 flake8==7.1.1
-pylint==3.3.1
\ No newline at end of file
+pylint==3.3.1
+timeout-decorator==0.5.0
\ No newline at end of file
diff --git a/src/pycomposefile/compose_element/compose_datatype_transformer.py b/src/pycomposefile/compose_element/compose_datatype_transformer.py
index d0915e0..2baf4ac 100644
--- a/src/pycomposefile/compose_element/compose_datatype_transformer.py
+++ b/src/pycomposefile/compose_element/compose_datatype_transformer.py
@@ -59,7 +59,7 @@ def update_value_with_resolved_environment(self, env_variable_name, env_variable
         return re.sub(env_variable_name, env_variable_value, source_string)
 
     def replace_environment_variables_with_empty_unset(self, value):
-        capture = re.compile(r"(\$+)\{(?P<variablename>\w+)\:-(?P<defaultvalue>.+)\}")
+        capture = re.compile(r"(\$+)\{(?P<variablename>\w+)\:-(?P<defaultvalue>[^$]*?)\}")
         matches = capture.search(value)
         if matches is not None and matches[1] == "$$":
             return value
@@ -68,7 +68,8 @@ def replace_environment_variables_with_empty_unset(self, value):
             default_value = matches.group("defaultvalue")
             if env_var is None or len(env_var) == 0:
                 env_var = default_value
-            value = self.update_value_with_resolved_environment(f"\\{matches[0]}", env_var, value)
+            escaped = re.sub(r"([*+?{}])", r"\\\1", matches[0]) # escape special characters
+            value = self.update_value_with_resolved_environment(f"\\{escaped}", env_var, value)
             matches = capture.search(value)
         return value
 
diff --git a/src/tests/environment_variable_evaluation/test_environment_variables_braces.py b/src/tests/environment_variable_evaluation/test_environment_variables_braces.py
index 50334d5..99c018e 100644
--- a/src/tests/environment_variable_evaluation/test_environment_variables_braces.py
+++ b/src/tests/environment_variable_evaluation/test_environment_variables_braces.py
@@ -2,7 +2,7 @@
 import os
 from ..compose_generator import ComposeGenerator
 from pycomposefile.compose_element import EmptyOrUnsetException
-
+import timeout_decorator
 
 class TestBracesNoUnderscoreNoDigitVariableInterpolation(TestCase):
 
@@ -19,6 +19,21 @@ def test_uppercase_with_default_when_unset_in_string_value(self):
         compose_file = ComposeGenerator.get_compose_with_string_value(braced_env_with_default_unset)
         self.assertEqual(compose_file.services["frontend"].image, "awesome/bob")
 
+    def test_uppercase_without_default_when_unset_in_string_value(self):
+        env_var = "DEFAULTUNSET"
+        os.unsetenv(env_var)
+        braced_env_with_default_unset = "{" + env_var + ":-}"
+        compose_file = ComposeGenerator.get_compose_with_string_value(braced_env_with_default_unset)
+        self.assertEqual(compose_file.services["frontend"].image, "awesome/")
+
+    @timeout_decorator.timeout(5)
+    def test_uppercase_with_nested_default_when_unset_in_string_value(self):
+        env_var = "DEFAULTUNSET"
+        os.unsetenv(env_var)
+        braced_env_with_default_unset = "{" + env_var + ":-${CHILDUNSET:-bob}}"
+        compose_file = ComposeGenerator.get_compose_with_string_value(braced_env_with_default_unset)
+        self.assertEqual(compose_file.services["frontend"].image, "awesome/bob")
+
     @mock.patch.dict(os.environ, {"TESTCPUCOUNT": "1.5"})
     def test_uppercase_in_decimal_value(self):
         braced_env_var = "{TESTCPUCOUNT}"
@@ -48,6 +63,21 @@ def test_lowercase_with_default_when_unset_in_string_value(self):
         compose_file = ComposeGenerator.get_compose_with_string_value(braced_env_with_default_unset)
         self.assertEqual(compose_file.services["frontend"].image, "awesome/bob")
 
+    def test_lowercase_without_default_when_unset_in_string_value(self):
+        env_var = "defaultunset"
+        os.unsetenv(env_var)
+        braced_env_with_default_unset = "{" + env_var + ":-}"
+        compose_file = ComposeGenerator.get_compose_with_string_value(braced_env_with_default_unset)
+        self.assertEqual(compose_file.services["frontend"].image, "awesome/")
+
+    @timeout_decorator.timeout(5)
+    def test_lowercase_with_nested_default_when_unset_in_string_value(self):
+        env_var = "defaultunset"
+        os.unsetenv(env_var)
+        braced_env_with_default_unset = "{" + env_var + ":-${childunset:-bob}}"
+        compose_file = ComposeGenerator.get_compose_with_string_value(braced_env_with_default_unset)
+        self.assertEqual(compose_file.services["frontend"].image, "awesome/bob")
+
     @mock.patch.dict(os.environ, {"testcpucount": "1.5"})
     def test_lowercase_in_decimal_value(self):
         braced_env_var = "{testcpucount}"
@@ -88,3 +118,86 @@ def test_service_with_double_dollar_sign_env_vars(self):
         compose_file = ComposeGenerator.get_compose_with_double_dollar_sign_env_vars()
 
         self.assertEqual(compose_file.services["frontend"].environment["ENVIRONMENT"], "$ENVIRONMENT")
+
+    @timeout_decorator.timeout(5)
+    def test_uppercase_with_asterisk_as_default(self):
+        env_var = "DEFAULTUNSET"
+        os.unsetenv(env_var)
+        braced_env_with_default_unset = "{" + env_var + ":-*}"
+        compose_file = ComposeGenerator.get_compose_with_string_value(braced_env_with_default_unset)
+        self.assertEqual(compose_file.services["frontend"].image, "awesome/*")
+
+    @timeout_decorator.timeout(5)
+    def test_uppercase_with_plus_as_default(self):
+        env_var = "DEFAULTUNSET"
+        os.unsetenv(env_var)
+        braced_env_with_default_unset = "{" + env_var + ":-+}"
+        compose_file = ComposeGenerator.get_compose_with_string_value(braced_env_with_default_unset)
+        self.assertEqual(compose_file.services["frontend"].image, "awesome/+")
+
+    @timeout_decorator.timeout(5)
+    def test_uppercase_with_question_as_default(self):
+        env_var = "DEFAULTUNSET"
+        os.unsetenv(env_var)
+        braced_env_with_default_unset = "{" + env_var + ":-?}"
+        compose_file = ComposeGenerator.get_compose_with_string_value(braced_env_with_default_unset)
+        self.assertEqual(compose_file.services["frontend"].image, "awesome/?")
+
+    @timeout_decorator.timeout(5)
+    def test_uppercase_with_rightbrace_as_default(self):
+        env_var = "DEFAULTUNSET"
+        os.unsetenv(env_var)
+        braced_env_with_default_unset = "{" + env_var + ":-a}-}"
+        compose_file = ComposeGenerator.get_compose_with_string_value(braced_env_with_default_unset)
+        self.assertEqual(compose_file.services["frontend"].image, "awesome/a-}") # 
+
+    @timeout_decorator.timeout(5)
+    def test_lowercase_with_asterisk_as_default(self):
+        env_var = "defaultunset"
+        os.unsetenv(env_var)
+        braced_env_with_default_unset = "{" + env_var + ":-*}"
+        compose_file = ComposeGenerator.get_compose_with_string_value(braced_env_with_default_unset)
+        self.assertEqual(compose_file.services["frontend"].image, "awesome/*")
+
+    @timeout_decorator.timeout(5)
+    def test_lowercase_with_plus_as_default(self):
+        env_var = "defaultunset"
+        os.unsetenv(env_var)
+        braced_env_with_default_unset = "{" + env_var + ":-+}"
+        compose_file = ComposeGenerator.get_compose_with_string_value(braced_env_with_default_unset)
+        self.assertEqual(compose_file.services["frontend"].image, "awesome/+")
+
+    @timeout_decorator.timeout(5)
+    def test_lowercase_with_question_as_default(self):
+        env_var = "defaultunset"
+        os.unsetenv(env_var)
+        braced_env_with_default_unset = "{" + env_var + ":-?}"
+        compose_file = ComposeGenerator.get_compose_with_string_value(braced_env_with_default_unset)
+        self.assertEqual(compose_file.services["frontend"].image, "awesome/?")
+
+    @timeout_decorator.timeout(5)
+    def test_lowercase_with_rightbrace_as_default(self):
+        env_var = "defaultunset"
+        os.unsetenv(env_var)
+        braced_env_with_default_unset = "{" + env_var + ":-}}"
+        compose_file = ComposeGenerator.get_compose_with_string_value(braced_env_with_default_unset)
+        self.assertEqual(compose_file.services["frontend"].image, "awesome/}")
+
+    @timeout_decorator.timeout(5)
+    def test_uppercase_two_variables_with_default_in_string_value(self):
+        braced_first_env_var = "{HOSTPORT:-8080}"
+        braced_second_env_var = "{CONTAINERPORT:-80}"
+        compose_file = ComposeGenerator.get_with_two_environment_variables_in_string_value(braced_first_env_var, braced_second_env_var)
+        self.assertEqual(f"{compose_file.services['frontend'].ports[0]}", "8080:80/tcp")
+        self.assertEqual(compose_file.services['frontend'].ports[0].published, "8080")
+        self.assertEqual(compose_file.services['frontend'].ports[0].target, "80")
+
+    @timeout_decorator.timeout(5)
+    def test_lowercase_two_variables_with_default_in_string_value(self):
+        braced_first_env_var = "{httpport:-8080}"
+        braced_second_env_var = "{containerport:-80}"
+        compose_file = ComposeGenerator.get_with_two_environment_variables_in_string_value(braced_first_env_var, braced_second_env_var)
+        self.assertEqual(f"{compose_file.services['frontend'].ports[0]}", "8080:80/tcp")
+        self.assertEqual(compose_file.services['frontend'].ports[0].published, "8080")
+        self.assertEqual(compose_file.services['frontend'].ports[0].target, "80")
+