diff --git a/pythran/analyses/__init__.py b/pythran/analyses/__init__.py
index 8560129b0..3c149f9b0 100644
--- a/pythran/analyses/__init__.py
+++ b/pythran/analyses/__init__.py
@@ -9,7 +9,7 @@
 import analyses.Foo
 """
 
-from .aliases import Aliases, StrictAliases
+from .aliases import Aliases, StrictAliases, InterproceduralAliases
 from .ancestors import Ancestors, AncestorsWithBody
 from .argument_effects import ArgumentEffects
 from .argument_read_once import ArgumentReadOnce
diff --git a/pythran/analyses/aliases.py b/pythran/analyses/aliases.py
index 1266b7cfd..523e7fa98 100644
--- a/pythran/analyses/aliases.py
+++ b/pythran/analyses/aliases.py
@@ -544,6 +544,11 @@ def visit_DictComp(self, node):
 
     # aliasing created by statements
 
+    def init_function_alias(self, node):
+        "each argument is bound to a different identifier"
+        self.aliases.update((arg.id, {arg})
+                            for arg in node.args.args)
+
     def visit_FunctionDef(self, node):
         '''
         Initialise aliasing default value before visiting.
@@ -558,8 +563,7 @@ def visit_FunctionDef(self, node):
         self.aliases.update((k, {v})
                             for k, v in self.global_declarations.items())
 
-        self.aliases.update((arg.id, {arg})
-                            for arg in node.args.args)
+        self.init_function_alias(node)
 
         self.generic_visit(node)
         if Aliases.RetId in self.aliases:
@@ -612,6 +616,27 @@ def merge_return_aliases(args):
 
             node.return_alias = merge_return_aliases
 
+    def visit_Assert(self, node):
+        self.generic_visit(node)
+
+        if not isinstance(node.test, ast.Compare):
+            return
+        if len(node.test.ops) != 1:
+            return
+        op = node.test.ops[0]
+        comparator = node.test.comparators[0]
+
+        if not isinstance(node.test.left, ast.Name):
+            return
+        if not isinstance(comparator, ast.Name):
+            return
+
+        if isinstance(op, ast.IsNot):
+            left_aliases = self.aliases[node.test.left.id]
+            right_aliases = self.aliases[comparator.id]
+            self.aliases[node.test.left.id] = self.aliases[node.test.left.id].difference(right_aliases)
+            right_aliases.difference_update(left_aliases)
+
     def visit_Assign(self, node):
         r'''
         Assignment creates aliasing between lhs and rhs
@@ -786,3 +811,14 @@ class StrictAliases(Aliases):
 
     def get_unbound_value_set(self):
         return set()
+
+
+class InterproceduralAliases(Aliases):
+    """
+    Gather aliases while assuming two different parameters can point to the same
+    value
+    """
+
+    def init_function_alias(self, node):
+        self.aliases.update((arg.id, set(node.args.args))
+                            for arg in node.args.args)
diff --git a/pythran/optimizations/fast_gexpr.py b/pythran/optimizations/fast_gexpr.py
index c52814f80..9c4d391b5 100644
--- a/pythran/optimizations/fast_gexpr.py
+++ b/pythran/optimizations/fast_gexpr.py
@@ -1,6 +1,6 @@
 """ Optimize a[...] = b[...] + c when we have no conflicting aliasing """
 
-from pythran.analyses import Aliases
+from pythran.analyses import InterproceduralAliases
 from pythran.passmanager import Transformation
 
 import gast as ast
@@ -10,7 +10,7 @@ class FastGExpr(Transformation):
 
     def __init__(self):
         self.update = False
-        super(FastGExpr, self).__init__(Aliases)
+        super(FastGExpr, self).__init__(InterproceduralAliases)
 
     def as_gexpr(self, node):
         if not isinstance(node, ast.Subscript):
@@ -39,7 +39,7 @@ def may_alias(self, gexpr, value):
         if isinstance(value, ast.Subscript):
             if not isinstance(value.value, ast.Name):
                 return True
-            return gexpr[0] in self.aliases[value.value]
+            return not self.interprocedural_aliases[gexpr[0]].isdisjoint(self.interprocedural_aliases[value.value])
 
         return True