diff --git a/pyhocon/__init__.py b/pyhocon/__init__.py
index 3c2bf132..939430ba 100644
--- a/pyhocon/__init__.py
+++ b/pyhocon/__init__.py
@@ -122,8 +122,6 @@ def convert_number(tokens):
         # ${path} or ${?path} for optional substitution
         SUBSTITUTION = "\$\{(?P<optional>\?)?(?P<variable>[^}]+)\}(?P<ws>\s*)"
 
-        substitutions = []
-
         def create_substitution(instring, loc, token):
             # remove the ${ and }
             match = re.match(SUBSTITUTION, token[0])
@@ -131,7 +129,6 @@ def create_substitution(instring, loc, token):
             ws = match.group('ws')
             optional = match.group('optional') == '?'
             substitution = ConfigSubstitution(variable, optional, ws, instring, loc)
-            substitutions.append(substitution)
             return substitution
 
         def include_config(token):
@@ -217,7 +214,7 @@ def include_config(token):
         # the file can be { ... } where {} can be omitted or []
         config_expr = ZeroOrMore(comment_eol | eol) + (list_expr | dict_expr | inside_dict_expr) + ZeroOrMore(comment_eol | eol_comma)
         config = config_expr.parseString(content, parseAll=True)[0]
-        ConfigParser._resolve_substitutions(config, substitutions)
+        ConfigParser._resolve_substitutions(config)
         return config
 
     @staticmethod
@@ -254,7 +251,29 @@ def _resolve_variable(config, substitution):
             return True, value
 
     @staticmethod
-    def _resolve_substitutions(config, substitutions):
+    def _resolve_substitutions(config):
+        # traverse config to find all the substitutions
+        def find_substitutions(item):
+            """Convert HOCON input into a JSON output
+
+            :return: JSON string representation
+            :type return: basestring
+            """
+            if isinstance(item, ConfigValues):
+                return item.get_substitutions()
+
+            substitutions = []
+            if isinstance(item, ConfigTree):
+                    for key, child in item.items():
+                        substitutions += find_substitutions(child)
+            elif isinstance(item, list):
+                for child in item:
+                    substitutions += find_substitutions(child)
+
+            return substitutions
+
+        substitutions = find_substitutions(config)
+
         if len(substitutions) > 0:
             _substitutions = set(substitutions)
             for i in range(len(substitutions)):
@@ -262,7 +281,7 @@ def _resolve_substitutions(config, substitutions):
                 for substitution in list(_substitutions):
                     is_optional_resolved, resolved_value = ConfigParser._resolve_variable(config, substitution)
 
-                    # if the substitition is optional
+                    # if the substitution is optional
                     if not is_optional_resolved and substitution.optional:
                         resolved_value = None
 
diff --git a/pyhocon/config_tree.py b/pyhocon/config_tree.py
index d045c7bb..21ef4333 100644
--- a/pyhocon/config_tree.py
+++ b/pyhocon/config_tree.py
@@ -264,7 +264,10 @@ def __init__(self, tokens, instring, loc):
             self.tokens[-1] = self.tokens[-1].rstrip()
 
     def has_substitution(self):
-        return next((True for token in self.tokens if isinstance(token, ConfigSubstitution)), False)
+        return len(self.get_substitutions()) > 0
+
+    def get_substitutions(self):
+        return [token for token in self.tokens if isinstance(token, ConfigSubstitution)]
 
     def transform(self):
         def determine_type(token):
diff --git a/tests/test_config_parser.py b/tests/test_config_parser.py
index c0dbb151..08a88f9b 100644
--- a/tests/test_config_parser.py
+++ b/tests/test_config_parser.py
@@ -1000,3 +1000,39 @@ def test_assign_dict_strings_no_equal_sign_with_eol(self):
         assert config['a'] == {'a': 1, 'b': 2}
         assert config['b'] == {'c': 3, 'd': 4}
         assert config['c'] == {'e': 5, 'f': 6}
+
+    def test_substitutions_overwrite(self):
+        config1 = ConfigFactory.parse_string(
+            """
+            a = 123
+            a = ${?test}
+            a = 5
+            """
+        )
+
+        assert config1['a'] == 5
+
+        config2 = ConfigFactory.parse_string(
+            """
+            {
+              database {
+                host = "localhost"
+                port = 8000
+                url = ${database.host}":"${database.port}
+              }
+
+              database {
+                host = ${?DB_HOST}
+              }
+
+              database {
+                host = "other.host.net"
+                port = 433
+              }
+            }
+            """
+        )
+
+        assert config2['database']['host'] == 'other.host.net'
+        assert config2['database']['port'] == 433
+        assert config2['database']['url'] == 'other.host.net:433'