diff --git a/clippy_lints/src/neg_cmp_op_on_partial_ord.rs b/clippy_lints/src/neg_cmp_op_on_partial_ord.rs
index 8e70d0eeba0..013bab69d79 100644
--- a/clippy_lints/src/neg_cmp_op_on_partial_ord.rs
+++ b/clippy_lints/src/neg_cmp_op_on_partial_ord.rs
@@ -1,7 +1,7 @@
 use rustc::hir::*;
 use rustc::lint::*;
 
-use crate::utils::{self, paths};
+use crate::utils::{self, paths, span_lint, in_external_macro};
 
 /// **What it does:**
 /// Checks for the usage of negated comparision operators on types which only implement
@@ -53,6 +53,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NoNegCompOpForPartialOrd {
     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
         if_chain! {
 
+            if !in_external_macro(cx, expr.span);
             if let Expr_::ExprUnary(UnOp::UnNot, ref inner) = expr.node;
             if let Expr_::ExprBinary(ref op, ref left, _) = inner.node;
             if let BinOp_::BiLe | BinOp_::BiGe | BinOp_::BiLt | BinOp_::BiGt = op.node;
@@ -78,7 +79,8 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NoNegCompOpForPartialOrd {
                 };
 
                 if implements_partial_ord && !implements_ord {
-                    cx.span_lint(
+                    span_lint(
+                        cx,
                         NEG_CMP_OP_ON_PARTIAL_ORD,
                         expr.span,
                         "The use of negated comparision operators on partially orded \
diff --git a/tests/ui/neg_cmp_op_on_partial_ord.rs b/tests/ui/neg_cmp_op_on_partial_ord.rs
index 214d627ba30..483972bb41b 100644
--- a/tests/ui/neg_cmp_op_on_partial_ord.rs
+++ b/tests/ui/neg_cmp_op_on_partial_ord.rs
@@ -1,6 +1,6 @@
-/// This test case utilizes `f64` an easy example for `PartialOrd` only types
-/// but the lint itself actually validates any expression where the left
-/// operand implements `PartialOrd` but not `Ord`.
+//! This test case utilizes `f64` an easy example for `PartialOrd` only types
+//! but the lint itself actually validates any expression where the left
+//! operand implements `PartialOrd` but not `Ord`.
 
 use std::cmp::Ordering;
 
@@ -54,5 +54,14 @@ fn main() {
     let _ = a_value <= another_value;
     let _ = a_value > another_value;
     let _ = a_value >= another_value;
-}
 
+    // --- regression tests ---
+
+    // Issue 2856: False positive on assert!()
+    //
+    // The macro always negates the result of the given comparision in its
+    // internal check which automatically triggered the lint. As it's an
+    // external macro there was no chance to do anything about it which lead
+    // to a whitelisting of all external macros.
+    assert!(a_value < another_value);
+}