diff --git a/lib/tokenize.cpp b/lib/tokenize.cpp
index 84fd46764..b608d1fb7 100644
--- a/lib/tokenize.cpp
+++ b/lib/tokenize.cpp
@@ -10247,6 +10247,31 @@ void Tokenizer::simplifyNestedNamespace()
     }
 }
 
+static bool sameTokens(const Token *first, const Token *last, const Token *other)
+{
+    while (other && first->str() == other->str()) {
+        if (first == last)
+            return true;
+        first = first->next();
+        other = other->next();
+    }
+
+    return false;
+}
+
+static Token * deleteAlias(Token * tok)
+{
+    Token::eraseTokens(tok, Token::findsimplematch(tok, ";"));
+
+    // delete first token
+    tok->deleteThis();
+
+    // delete ';' if not last token
+    tok->deleteThis();
+
+    return tok;
+}
+
 void Tokenizer::simplifyNamespaceAliases()
 {
     if (!isCPP())
@@ -10281,6 +10306,28 @@ void Tokenizer::simplifyNamespaceAliases()
                 else if (Token::simpleMatch(tok2, "}"))
                     endScope--;
                 else if (tok2->str() == name) {
+                    if (Token::Match(tok2->previous(), "namespace %name% =")) {
+                        // check for possible duplicate aliases
+                        if (sameTokens(tokNameStart, tokNameEnd, tok2->tokAt(2))) {
+                            // delete duplicate
+                            tok2 = deleteAlias(tok2->previous());
+                            continue;
+                        } else {
+                            // conflicting declaration (syntax error)
+                            if (endScope == scope) {
+                                // delete conflicting declaration
+                                tok2 = deleteAlias(tok2->previous());
+                            }
+
+                            // new declaration
+                            else {
+                                // TODO: use the new alias in this scope
+                                tok2 = deleteAlias(tok2->previous());
+                            }
+                            continue;
+                        }
+                    }
+
                     tok2->str(tokNameStart->str());
                     Token * tok3 = tokNameStart;
                     while (tok3 != tokNameEnd) {
diff --git a/test/testsimplifytokens.cpp b/test/testsimplifytokens.cpp
index 5fd61ab41..79a026006 100644
--- a/test/testsimplifytokens.cpp
+++ b/test/testsimplifytokens.cpp
@@ -3546,6 +3546,38 @@ private:
                       tok("using namespace std; namespace ios = boost::iostreams;"));
         ASSERT_EQUALS("namespace NS { boost :: iostreams :: istream foo ( \"foo\" ) ; }",
                       tok("namespace NS { using namespace std; namespace ios = boost::iostreams; ios::istream foo(\"foo\"); }"));
+
+        // duplicate namespace aliases
+        ASSERT_EQUALS(";",
+                      tok("namespace ios = boost::iostreams;\nnamespace ios = boost::iostreams;"));
+        ASSERT_EQUALS(";",
+                      tok("namespace ios = boost::iostreams;\nnamespace ios = boost::iostreams;\nnamespace ios = boost::iostreams;"));
+        ASSERT_EQUALS("namespace A { namespace B { void foo ( ) { bar ( A :: B :: ab ( ) ) ; } } }",
+                      tok("namespace A::B {"
+                          "namespace AB = A::B;"
+                          "void foo() {"
+                          "    namespace AB = A::B;" // duplicate declaration
+                          "    bar(AB::ab());"
+                          "}"
+                          "namespace AB = A::B;" //duplicate declaration
+                          "}"));
+
+        // redeclared nested namespace aliases
+        TODO_ASSERT_EQUALS("namespace A { namespace B { void foo ( ) { bar ( A :: B :: ab ( ) ) ; { baz ( A :: a ( ) ) ; } bar ( A :: B :: ab ( ) ) ; } } }",
+                           "namespace A { namespace B { void foo ( ) { bar ( A :: B :: ab ( ) ) ; { baz ( A :: B :: a ( ) ) ; } bar ( A :: B :: ab ( ) ) ; } } }",
+                           tok("namespace A::B {"
+                               "namespace AB = A::B;"
+                               "void foo() {"
+                               "    namespace AB = A::B;" // duplicate declaration
+                               "    bar(AB::ab());"
+                               "    {"
+                               "         namespace AB = A;"
+                               "         baz(AB::a());" // redeclaration OK
+                               "    }"
+                               "    bar(AB::ab());"
+                               "}"
+                               "namespace AB = A::B;" //duplicate declaration
+                               "}"));
     }
 };