diff --git a/src/librustdoc/test.rs b/src/librustdoc/test.rs
index 50acde64cf023..84ce9f6d2574d 100644
--- a/src/librustdoc/test.rs
+++ b/src/librustdoc/test.rs
@@ -395,6 +395,7 @@ pub fn make_test(s: &str,
     // Now push any outer attributes from the example, assuming they
     // are intended to be crate attributes.
     prog.push_str(&crate_attrs);
+    prog.push_str(&crates);
 
     // Uses libsyntax to parse the doctest and find if there's a main fn and the extern
     // crate already is included.
@@ -488,37 +489,78 @@ pub fn make_test(s: &str,
         prog.push_str("\n}");
     }
 
+    debug!("final doctest:\n{}", prog);
+
     (prog, line_offset)
 }
 
 // FIXME(aburka): use a real parser to deal with multiline attributes
 fn partition_source(s: &str) -> (String, String, String) {
-    let mut after_header = false;
+    #[derive(Copy, Clone, PartialEq)]
+    enum PartitionState {
+        Attrs,
+        Crates,
+        Other,
+    }
+    let mut state = PartitionState::Attrs;
     let mut before = String::new();
     let mut crates = String::new();
     let mut after = String::new();
 
     for line in s.lines() {
         let trimline = line.trim();
-        let header = trimline.chars().all(|c| c.is_whitespace()) ||
-            trimline.starts_with("#![") ||
-            trimline.starts_with("#[macro_use] extern crate") ||
-            trimline.starts_with("extern crate");
-        if !header || after_header {
-            after_header = true;
-            after.push_str(line);
-            after.push_str("\n");
-        } else {
-            if trimline.starts_with("#[macro_use] extern crate")
-                || trimline.starts_with("extern crate") {
+
+        // FIXME(misdreavus): if a doc comment is placed on an extern crate statement, it will be
+        // shunted into "everything else"
+        match state {
+            PartitionState::Attrs => {
+                state = if trimline.starts_with("#![") ||
+                    trimline.chars().all(|c| c.is_whitespace()) ||
+                    (trimline.starts_with("//") && !trimline.starts_with("///"))
+                {
+                    PartitionState::Attrs
+                } else if trimline.starts_with("extern crate") ||
+                    trimline.starts_with("#[macro_use] extern crate")
+                {
+                    PartitionState::Crates
+                } else {
+                    PartitionState::Other
+                };
+            }
+            PartitionState::Crates => {
+                state = if trimline.starts_with("extern crate") ||
+                    trimline.starts_with("#[macro_use] extern crate") ||
+                    trimline.chars().all(|c| c.is_whitespace()) ||
+                    (trimline.starts_with("//") && !trimline.starts_with("///"))
+                {
+                    PartitionState::Crates
+                } else {
+                    PartitionState::Other
+                };
+            }
+            PartitionState::Other => {}
+        }
+
+        match state {
+            PartitionState::Attrs => {
+                before.push_str(line);
+                before.push_str("\n");
+            }
+            PartitionState::Crates => {
                 crates.push_str(line);
                 crates.push_str("\n");
             }
-            before.push_str(line);
-            before.push_str("\n");
+            PartitionState::Other => {
+                after.push_str(line);
+                after.push_str("\n");
+            }
         }
     }
 
+    debug!("before:\n{}", before);
+    debug!("crates:\n{}", crates);
+    debug!("after:\n{}", after);
+
     (before, after, crates)
 }
 
@@ -1035,8 +1077,8 @@ fn main() {
 assert_eq!(2+2, 4);";
         let expected =
 "#![allow(unused)]
-fn main() {
 //Ceci n'est pas une `fn main`
+fn main() {
 assert_eq!(2+2, 4);
 }".to_string();
         let output = make_test(input, None, false, &opts);
@@ -1083,8 +1125,8 @@ assert_eq!(2+2, 4);";
 
         let expected =
 "#![allow(unused)]
-fn main() {
 // fn main
+fn main() {
 assert_eq!(2+2, 4);
 }".to_string();
 
diff --git a/src/test/rustdoc/comment-in-doctest.rs b/src/test/rustdoc/comment-in-doctest.rs
new file mode 100644
index 0000000000000..3468bb7bda473
--- /dev/null
+++ b/src/test/rustdoc/comment-in-doctest.rs
@@ -0,0 +1,30 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags:--test
+
+// comments, both doc comments and regular ones, used to trick rustdoc's doctest parser into
+// thinking that everything after it was part of the regular program. combined with the libsyntax
+// parser loop failing to detect the manual main function, it would wrap everything in `fn main`,
+// which would cause the doctest to fail as the "extern crate" declaration was no longer valid.
+// oddly enough, it would pass in 2018 if a crate was in the extern prelude. see
+// https://github.com/rust-lang/rust/issues/56727
+
+//! ```
+//! // crate: proc-macro-test
+//! //! this is a test
+//!
+//! // used to pull in proc-macro specific items
+//! extern crate proc_macro;
+//!
+//! use proc_macro::TokenStream;
+//!
+//! # fn main() {}
+//! ```