diff --git a/src/doc/rustc/src/command-line-arguments.md b/src/doc/rustc/src/command-line-arguments.md
index 79b4f7542f9..5887a0869e6 100644
--- a/src/doc/rustc/src/command-line-arguments.md
+++ b/src/doc/rustc/src/command-line-arguments.md
@@ -264,7 +264,12 @@ This flag, when combined with other flags, makes them produce extra output.
 
 This flag allows you to pass the name and location of an external crate that
 will be linked into the crate you are building. This flag may be specified
-multiple times. The format of the value should be `CRATENAME=PATH`.
+multiple times. This flag takes an argument with either of the following
+formats:
+
+* `CRATENAME=PATH` — Indicates the given crate is found at the given path.
+* `CRATENAME` — Indicates the given crate may be found in the search path,
+  such as within the sysroot or via the `-L` flag.
 
 <a id="option-sysroot"></a>
 ## `--sysroot`: Override the system root
diff --git a/src/librustc/session/config.rs b/src/librustc/session/config.rs
index 2bcddeaf196..1740d8fe967 100644
--- a/src/librustc/session/config.rs
+++ b/src/librustc/session/config.rs
@@ -2392,13 +2392,6 @@ fn parse_externs(
         let name = parts.next().unwrap_or_else(||
             early_error(error_format, "--extern value must not be empty"));
         let location = parts.next().map(|s| s.to_string());
-        if location.is_none() && !is_unstable_enabled {
-            early_error(
-                error_format,
-                "the `-Z unstable-options` flag must also be passed to \
-                 enable `--extern crate_name` without `=path`",
-            );
-        };
 
         let entry = externs
             .entry(name.to_owned())
diff --git a/src/librustdoc/config.rs b/src/librustdoc/config.rs
index 0b8d4d6c302..255d5f9f35d 100644
--- a/src/librustdoc/config.rs
+++ b/src/librustdoc/config.rs
@@ -615,10 +615,6 @@ fn parse_externs(matches: &getopts::Matches) -> Result<Externs, String> {
         let mut parts = arg.splitn(2, '=');
         let name = parts.next().ok_or("--extern value must not be empty".to_string())?;
         let location = parts.next().map(|s| s.to_string());
-        if location.is_none() && !nightly_options::is_unstable_enabled(matches) {
-            return Err("the `-Z unstable-options` flag must also be passed to \
-                        enable `--extern crate_name` without `=path`".to_string());
-        }
         let name = name.to_string();
         // For Rustdoc purposes, we can treat all externs as public
         externs.entry(name)
diff --git a/src/test/run-make-fulldeps/extern-flag-fun/Makefile b/src/test/run-make-fulldeps/extern-flag-fun/Makefile
index a9f25853350..7f54d6ea3bc 100644
--- a/src/test/run-make-fulldeps/extern-flag-fun/Makefile
+++ b/src/test/run-make-fulldeps/extern-flag-fun/Makefile
@@ -4,7 +4,6 @@ all:
 	$(RUSTC) bar.rs --crate-type=rlib
 	$(RUSTC) bar.rs --crate-type=rlib -C extra-filename=-a
 	$(RUSTC) bar-alt.rs --crate-type=rlib
-	$(RUSTC) foo.rs --extern hello && exit 1 || exit 0
 	$(RUSTC) foo.rs --extern bar=no-exist && exit 1 || exit 0
 	$(RUSTC) foo.rs --extern bar=foo.rs && exit 1 || exit 0
 	$(RUSTC) foo.rs \
diff --git a/src/test/run-make-fulldeps/save-analysis-rfc2126/Makefile b/src/test/run-make-fulldeps/save-analysis-rfc2126/Makefile
index bf98fcd10cf..36288c4b870 100644
--- a/src/test/run-make-fulldeps/save-analysis-rfc2126/Makefile
+++ b/src/test/run-make-fulldeps/save-analysis-rfc2126/Makefile
@@ -1,8 +1,7 @@
 -include ../tools.mk
 
 all: extern_absolute_paths.rs krate2
-	$(RUSTC) extern_absolute_paths.rs -Zsave-analysis --edition=2018 \
-		-Z unstable-options --extern krate2
+	$(RUSTC) extern_absolute_paths.rs -Zsave-analysis --edition=2018 --extern krate2
 	cat $(TMPDIR)/save-analysis/extern_absolute_paths.json | "$(PYTHON)" validate_json.py
 
 krate2: krate2.rs