diff --git a/jedi/evaluate/context/instance.py b/jedi/evaluate/context/instance.py
index 51d935ea..49ad3e9f 100644
--- a/jedi/evaluate/context/instance.py
+++ b/jedi/evaluate/context/instance.py
@@ -15,23 +15,27 @@ from jedi.evaluate.context import iterable
 from jedi.parser_utils import get_parent_scope
 
 
-
-class InstanceFunctionExecution(FunctionExecutionContext):
-    def __init__(self, instance, parent_context, function_context, var_args):
+class BaseInstanceFunctionExecution(FunctionExecutionContext):
+    def __init__(self, instance, *args, **kwargs):
         self.instance = instance
+        super(BaseInstanceFunctionExecution, self).__init__(
+            instance.evaluator, *args, **kwargs)
+
+
+class InstanceFunctionExecution(BaseInstanceFunctionExecution):
+    def __init__(self, instance, parent_context, function_context, var_args):
         var_args = InstanceVarArgs(self, var_args)
 
         super(InstanceFunctionExecution, self).__init__(
-            instance.evaluator, parent_context, function_context, var_args)
+            instance, parent_context, function_context, var_args)
 
 
-class AnonymousInstanceFunctionExecution(FunctionExecutionContext):
+class AnonymousInstanceFunctionExecution(BaseInstanceFunctionExecution):
     function_execution_filter = filters.AnonymousInstanceFunctionExecutionFilter
 
     def __init__(self, instance, parent_context, function_context, var_args):
-        self.instance = instance
         super(AnonymousInstanceFunctionExecution, self).__init__(
-            instance.evaluator, parent_context, function_context, var_args)
+            instance, parent_context, function_context, var_args)
 
 
 class AbstractInstanceContext(Context):
diff --git a/jedi/evaluate/pep0484.py b/jedi/evaluate/pep0484.py
index 10edcb8e..b0bc0413 100644
--- a/jedi/evaluate/pep0484.py
+++ b/jedi/evaluate/pep0484.py
@@ -140,11 +140,19 @@ def infer_param(execution_context, param):
         # If the number of parameters doesn't match length of type comment,
         # ignore first parameter (assume it's self).
         if len(params_comments) != len(all_params):
+            debug.warning(
+                "Comments length != Params length %s %s",
+                params_comments, all_params
+            )
+        from jedi.evaluate.context.instance import BaseInstanceFunctionExecution
+        if isinstance(execution_context, BaseInstanceFunctionExecution):
             if index == 0:
                 # Assume it's self, which is already handled
                 return NO_CONTEXTS
-            else:
-                index -= 1
+            index -= 1
+        if index >= len(params_comments):
+            return NO_CONTEXTS
+
         param_comment = params_comments[index]
         # Construct annotation from type comment
         annotation = tree.String(repr(param_comment), node.start_pos)
diff --git a/test/completion/pep0484_comments.py b/test/completion/pep0484_comments.py
index 816cc736..9f0661ec 100644
--- a/test/completion/pep0484_comments.py
+++ b/test/completion/pep0484_comments.py
@@ -178,3 +178,9 @@ def x(a, b):
     # type: (1) -> a
     #?
     a
+def x(a, b, c):
+    # type: (str) -> a
+    #?
+    b
+    #?
+    c