diff --git a/lib/checkbufferoverrun.cpp b/lib/checkbufferoverrun.cpp
index bddf1fdb2..cbce6bb60 100644
--- a/lib/checkbufferoverrun.cpp
+++ b/lib/checkbufferoverrun.cpp
@@ -1596,15 +1596,15 @@ void CheckBufferOverrun::negativeIndex()
         const long index = MathLib::toLongNumber(tok->next()->str());
         if (index < 0)
         {
-            // Multidimensional index => error
-            if (Token::simpleMatch(tok->previous(), "]") || Token::simpleMatch(tok->tokAt(3), "["))
-                negativeIndexError(tok, index);
+            // Negative index. Check if it's an array.
+            const Token *tok2 = tok;
+            while (Token::simpleMatch(tok2->previous(), "]"))
+                tok2 = tok2->previous()->link();
 
-            // 1-dimensional array => error
-            else if (tok->previous() && tok->previous()->varId())
+            if (tok2->previous() && tok2->previous()->varId())
             {
-                const Token *tok2 = Token::findmatch(_tokenizer->tokens(), "%varid%", tok->previous()->varId());
-                if (tok2 && Token::Match(tok2->next(), "[ %any% ] ;"))
+                const Token *tok3 = Token::findmatch(_tokenizer->tokens(), "%varid%", tok2->previous()->varId());
+                if (tok3 && Token::Match(tok3->next(), "[ %any% ] ;|["))
                     negativeIndexError(tok, index);
             }
         }
diff --git a/test/testbufferoverrun.cpp b/test/testbufferoverrun.cpp
index 6a1cb8522..b175e254c 100644
--- a/test/testbufferoverrun.cpp
+++ b/test/testbufferoverrun.cpp
@@ -1155,6 +1155,13 @@ private:
               "    if (p[-1]);\n"
               "}\n");
         ASSERT_EQUALS("", errout.str());
+
+        // ticket #1850
+        check("int f(const std::map<int, std::map<int,int> > &m)\n"
+              "{\n"
+              "    return m[0][-1];\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void array_index_for_decr()