diff --git a/clippy_lints/src/assertions_on_constants.rs b/clippy_lints/src/assertions_on_constants.rs
index ceea913233ee..36ed835e2581 100644
--- a/clippy_lints/src/assertions_on_constants.rs
+++ b/clippy_lints/src/assertions_on_constants.rs
@@ -2,9 +2,9 @@ use if_chain::if_chain;
 use rustc::hir::{Expr, ExprKind};
 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
 use rustc::{declare_lint_pass, declare_tool_lint};
+use syntax_pos::Span;
 
 use crate::consts::{constant, Constant};
-use crate::syntax::ast::LitKind;
 use crate::utils::{in_macro, is_direct_expn_of, span_help_and_lint};
 
 declare_clippy_lint! {
@@ -33,41 +33,40 @@ declare_lint_pass!(AssertionsOnConstants => [ASSERTIONS_ON_CONSTANTS]);
 
 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for AssertionsOnConstants {
     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
+        let mut is_debug_assert = false;
+        let debug_assert_not_in_macro = |span: Span| {
+            is_debug_assert = true;
+            // Check that `debug_assert!` itself is not inside a macro
+            !in_macro(span)
+        };
         if_chain! {
             if let Some(assert_span) = is_direct_expn_of(e.span, "assert");
             if !in_macro(assert_span)
-                || is_direct_expn_of(assert_span, "debug_assert").map_or(false, |span| !in_macro(span));
+                || is_direct_expn_of(assert_span, "debug_assert")
+                    .map_or(false, debug_assert_not_in_macro);
             if let ExprKind::Unary(_, ref lit) = e.node;
+            if let Some(bool_const) = constant(cx, cx.tables, lit);
             then {
-                if let ExprKind::Lit(ref inner) = lit.node {
-                    match inner.node {
-                        LitKind::Bool(true) => {
-                            span_help_and_lint(cx, ASSERTIONS_ON_CONSTANTS, e.span,
-                                "assert!(true) will be optimized out by the compiler",
-                                "remove it");
-                        },
-                        LitKind::Bool(false) => {
-                            span_help_and_lint(
-                                cx, ASSERTIONS_ON_CONSTANTS, e.span,
-                                "assert!(false) should probably be replaced",
-                                "use panic!() or unreachable!()");
-                        },
-                        _ => (),
-                    }
-                } else if let Some(bool_const) = constant(cx, cx.tables, lit) {
-                    match bool_const.0 {
-                        Constant::Bool(true) => {
-                            span_help_and_lint(cx, ASSERTIONS_ON_CONSTANTS, e.span,
-                                "assert!(const: true) will be optimized out by the compiler",
-                                "remove it");
-                        },
-                        Constant::Bool(false) => {
-                            span_help_and_lint(cx, ASSERTIONS_ON_CONSTANTS, e.span,
-                                "assert!(const: false) should probably be replaced",
-                                "use panic!() or unreachable!()");
-                        },
-                        _ => (),
-                    }
+                match bool_const.0 {
+                    Constant::Bool(true) => {
+                        span_help_and_lint(
+                            cx,
+                            ASSERTIONS_ON_CONSTANTS,
+                            e.span,
+                            "`assert!(true)` will be optimized out by the compiler",
+                            "remove it"
+                        );
+                    },
+                    Constant::Bool(false) if !is_debug_assert => {
+                        span_help_and_lint(
+                            cx,
+                            ASSERTIONS_ON_CONSTANTS,
+                            e.span,
+                            "`assert!(false)` should probably be replaced",
+                            "use `panic!()` or `unreachable!()`"
+                        );
+                    },
+                    _ => (),
                 }
             }
         }
diff --git a/tests/ui/assertions_on_constants.rs b/tests/ui/assertions_on_constants.rs
index 0d2953c7ed81..aee6cc505abd 100644
--- a/tests/ui/assertions_on_constants.rs
+++ b/tests/ui/assertions_on_constants.rs
@@ -18,6 +18,8 @@ fn main() {
     assert!(C);
 
     debug_assert!(true);
+    // Don't lint this, since there is no better way for expressing "Only panic in debug mode".
+    debug_assert!(false); // #3948
     assert_const!(3);
     assert_const!(-1);
 }
diff --git a/tests/ui/assertions_on_constants.stderr b/tests/ui/assertions_on_constants.stderr
index adfa326abacb..c22da856975c 100644
--- a/tests/ui/assertions_on_constants.stderr
+++ b/tests/ui/assertions_on_constants.stderr
@@ -1,4 +1,4 @@
-error: assert!(true) will be optimized out by the compiler
+error: `assert!(true)` will be optimized out by the compiler
   --> $DIR/assertions_on_constants.rs:9:5
    |
 LL |     assert!(true);
@@ -7,15 +7,15 @@ LL |     assert!(true);
    = note: `-D clippy::assertions-on-constants` implied by `-D warnings`
    = help: remove it
 
-error: assert!(false) should probably be replaced
+error: `assert!(false)` should probably be replaced
   --> $DIR/assertions_on_constants.rs:10:5
    |
 LL |     assert!(false);
    |     ^^^^^^^^^^^^^^^
    |
-   = help: use panic!() or unreachable!()
+   = help: use `panic!()` or `unreachable!()`
 
-error: assert!(true) will be optimized out by the compiler
+error: `assert!(true)` will be optimized out by the compiler
   --> $DIR/assertions_on_constants.rs:11:5
    |
 LL |     assert!(true, "true message");
@@ -23,15 +23,15 @@ LL |     assert!(true, "true message");
    |
    = help: remove it
 
-error: assert!(false) should probably be replaced
+error: `assert!(false)` should probably be replaced
   --> $DIR/assertions_on_constants.rs:12:5
    |
 LL |     assert!(false, "false message");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = help: use panic!() or unreachable!()
+   = help: use `panic!()` or `unreachable!()`
 
-error: assert!(const: true) will be optimized out by the compiler
+error: `assert!(true)` will be optimized out by the compiler
   --> $DIR/assertions_on_constants.rs:15:5
    |
 LL |     assert!(B);
@@ -39,15 +39,15 @@ LL |     assert!(B);
    |
    = help: remove it
 
-error: assert!(const: false) should probably be replaced
+error: `assert!(false)` should probably be replaced
   --> $DIR/assertions_on_constants.rs:18:5
    |
 LL |     assert!(C);
    |     ^^^^^^^^^^^
    |
-   = help: use panic!() or unreachable!()
+   = help: use `panic!()` or `unreachable!()`
 
-error: assert!(true) will be optimized out by the compiler
+error: `assert!(true)` will be optimized out by the compiler
   --> $DIR/assertions_on_constants.rs:20:5
    |
 LL |     debug_assert!(true);