diff --git a/src/ops/cargo_doc.rs b/src/ops/cargo_doc.rs
index ce219328c5a..9292c8a7458 100644
--- a/src/ops/cargo_doc.rs
+++ b/src/ops/cargo_doc.rs
@@ -159,6 +159,7 @@ fn merge_cross_crate_info(ws: &Workspace<'_>, compilation: &Compilation<'_>) ->
             cmd.arg("-o")
                 .arg(rustdoc_artifact_dir.as_path_unlocked())
                 .arg("-Zunstable-options");
+            cmd.arg("--edition=2015"); // to suppress edition unspecified warning
             cmd.args(&compilation.rustdocflags[kind]);
             for parts_dir in doc_parts_dirs {
                 let mut include_arg = OsString::from("--read-doc-meta-dir=");
diff --git a/tests/testsuite/doc.rs b/tests/testsuite/doc.rs
index eb7d848ab3c..eb1810a2b6e 100644
--- a/tests/testsuite/doc.rs
+++ b/tests/testsuite/doc.rs
@@ -3286,7 +3286,7 @@ fn mergeable_info_with_deps() {
 [RUNNING] `rustdoc [..]--crate-name foo [..]--write-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out[..]`
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 [MERGING] 2 docs for host
-[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --read-doc-meta-dir=[ROOT]/foo/target/debug/build/dep/[HASH]/out --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
+[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --edition=2015 --read-doc-meta-dir=[ROOT]/foo/target/debug/build/dep/[HASH]/out --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
 [FINISHED] documentation merge in [ELAPSED]s
 [GENERATED] [ROOT]/foo/target/doc/foo/index.html
 
@@ -3333,7 +3333,7 @@ fn mergeable_info_with_rustdocflags() {
 [RUNNING] `rustdoc [..]--crate-name foo [..]-o [ROOT]/foo/target/doc [..]-Zunstable-options --write-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out [..]--markdown-playground-url=example.com --crate-version 0.5.0`
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 [MERGING] 1 doc for host
-[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --markdown-playground-url=example.com --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
+[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --edition=2015 --markdown-playground-url=example.com --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
 [FINISHED] documentation merge in [ELAPSED]s
 [GENERATED] [ROOT]/foo/target/doc/foo/index.html
 
@@ -3372,7 +3372,7 @@ fn mergeable_info_no_deps() {
 [RUNNING] `rustdoc [..]--crate-name foo [..]--write-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out [..]`
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 [MERGING] 1 doc for host
-[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
+[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --edition=2015 --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
 [FINISHED] documentation merge in [ELAPSED]s
 [GENERATED] [ROOT]/foo/target/doc/foo/index.html
 
@@ -3443,7 +3443,7 @@ fn mergeable_info_workspace() {
 [RUNNING] `rustdoc [..]--crate-name foo [..]--write-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out [..]`
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 [MERGING] 3 docs for host
-[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --read-doc-meta-dir=[ROOT]/foo/target/debug/build/bar/[HASH]/out --read-doc-meta-dir=[ROOT]/foo/target/debug/build/dep/[HASH]/out --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
+[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --edition=2015 --read-doc-meta-dir=[ROOT]/foo/target/debug/build/bar/[HASH]/out --read-doc-meta-dir=[ROOT]/foo/target/debug/build/dep/[HASH]/out --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
 [FINISHED] documentation merge in [ELAPSED]s
 [GENERATED] [ROOT]/foo/target/doc/bar/index.html
 [GENERATED] [ROOT]/foo/target/doc/dep/index.html
@@ -3508,9 +3508,9 @@ fn mergeable_info_multi_targets() {
 [RUNNING] `rustdoc [..]--crate-name foo src/lib.rs --target [ALT_TARGET] [..]--write-doc-meta-dir=[ROOT]/foo/target/[ALT_TARGET]/debug/build/foo/[HASH]/out [..]`
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 [MERGING] 1 doc for [ALT_TARGET]
-[RUNNING] `rustdoc -o [ROOT]/foo/target/[ALT_TARGET]/doc -Zunstable-options --read-doc-meta-dir=[ROOT]/foo/target/[ALT_TARGET]/debug/build/foo/[HASH]/out`
+[RUNNING] `rustdoc -o [ROOT]/foo/target/[ALT_TARGET]/doc -Zunstable-options --edition=2015 --read-doc-meta-dir=[ROOT]/foo/target/[ALT_TARGET]/debug/build/foo/[HASH]/out`
 [MERGING] 1 doc for [HOST_TARGET]
-[RUNNING] `rustdoc -o [ROOT]/foo/target/[HOST_TARGET]/doc -Zunstable-options --read-doc-meta-dir=[ROOT]/foo/target/[HOST_TARGET]/debug/build/foo/[HASH]/out`
+[RUNNING] `rustdoc -o [ROOT]/foo/target/[HOST_TARGET]/doc -Zunstable-options --edition=2015 --read-doc-meta-dir=[ROOT]/foo/target/[HOST_TARGET]/debug/build/foo/[HASH]/out`
 [FINISHED] documentation merge in [ELAPSED]s
 [GENERATED] [ROOT]/foo/target/[HOST_TARGET]/doc/foo/index.html
 [GENERATED] [ROOT]/foo/target/[ALT_TARGET]/doc/foo/index.html
@@ -3580,7 +3580,7 @@ fn mergeable_info_rebuild_detection() {
 [RUNNING] `rustdoc [..]--crate-name foo [..]--write-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out [..]`
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 [MERGING] 1 doc for host
-[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
+[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --edition=2015 --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
 [FINISHED] documentation merge in [ELAPSED]s
 [GENERATED] [ROOT]/foo/target/doc/foo/index.html
 
@@ -3646,7 +3646,7 @@ fn mergeable_info_rebuild_detection() {
 [RUNNING] `rustdoc [..]--crate-name foo [..]--write-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out [..]`
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 [MERGING] 1 doc for host
-[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
+[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --edition=2015 --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
 [FINISHED] documentation merge in [ELAPSED]s
 [GENERATED] [ROOT]/foo/target/doc/foo/index.html
 
@@ -3724,7 +3724,7 @@ fn mergeable_info_rebuild_with_depinfo() {
 [RUNNING] `rustdoc [..]--crate-name foo [..]--emit=html-non-static-files,dep-info=[..] --write-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out [..]`
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 [MERGING] 1 doc for host
-[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
+[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --edition=2015 --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
 [FINISHED] documentation merge in [ELAPSED]s
 [GENERATED] [ROOT]/foo/target/doc/foo/index.html
 
@@ -3792,7 +3792,7 @@ fn mergeable_info_rebuild_with_depinfo() {
 [RUNNING] `rustdoc [..]--crate-name foo [..]--emit=html-non-static-files,dep-info=[..] --write-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out [..]`
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 [MERGING] 1 doc for host
-[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
+[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --edition=2015 --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
 [FINISHED] documentation merge in [ELAPSED]s
 [GENERATED] [ROOT]/foo/target/doc/foo/index.html
 
@@ -3885,7 +3885,7 @@ fn mergeable_info_additive() {
 [RUNNING] `rustdoc [..]--crate-name foo [..]--write-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out [..]`
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 [MERGING] 1 doc for host
-[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
+[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --edition=2015 --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
 [FINISHED] documentation merge in [ELAPSED]s
 [GENERATED] [ROOT]/foo/target/doc/foo/index.html
 
@@ -3922,7 +3922,7 @@ fn mergeable_info_additive() {
 [RUNNING] `rustdoc [..]--crate-name dep [..]--write-doc-meta-dir=[ROOT]/foo/target/debug/build/dep/[HASH]/out [..]`
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 [MERGING] 2 docs for host
-[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --read-doc-meta-dir=[ROOT]/foo/target/debug/build/dep/[HASH]/out --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
+[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --edition=2015 --read-doc-meta-dir=[ROOT]/foo/target/debug/build/dep/[HASH]/out --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
 [FINISHED] documentation merge in [ELAPSED]s
 [GENERATED] [ROOT]/foo/target/doc/dep/index.html
 
@@ -3960,7 +3960,7 @@ fn mergeable_info_additive() {
 [RUNNING] `rustdoc [..]--crate-name bar [..]--write-doc-meta-dir=[ROOT]/foo/target/debug/build/bar/[HASH]/out [..]`
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 [MERGING] 3 docs for host
-[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --read-doc-meta-dir=[ROOT]/foo/target/debug/build/bar/[HASH]/out --read-doc-meta-dir=[ROOT]/foo/target/debug/build/dep/[HASH]/out --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
+[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --edition=2015 --read-doc-meta-dir=[ROOT]/foo/target/debug/build/bar/[HASH]/out --read-doc-meta-dir=[ROOT]/foo/target/debug/build/dep/[HASH]/out --read-doc-meta-dir=[ROOT]/foo/target/debug/build/foo/[HASH]/out`
 [FINISHED] documentation merge in [ELAPSED]s
 [GENERATED] [ROOT]/foo/target/doc/bar/index.html
 
@@ -4040,7 +4040,7 @@ From [ROOTURL]/registry
 [RUNNING] `rustdoc [..]--crate-name dep [..]--write-doc-meta-dir=[ROOT]/foo/target/debug/build/dep/[HASH]/out [..]--crate-version 0.1.0`
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 [MERGING] 1 doc for host
-[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --read-doc-meta-dir=[ROOT]/foo/target/debug/build/dep/[HASH]/out`
+[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --edition=2015 --read-doc-meta-dir=[ROOT]/foo/target/debug/build/dep/[HASH]/out`
 [FINISHED] documentation merge in [ELAPSED]s
 [GENERATED] [ROOT]/foo/target/doc/dep/index.html
 
@@ -4080,7 +4080,7 @@ From [ROOTURL]/registry
 [RUNNING] `rustdoc [..]--crate-name dep [..]--write-doc-meta-dir=[ROOT]/foo/target/debug/build/dep/[HASH]/out [..]--crate-version 0.2.0`
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 [MERGING] 1 doc for host
-[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --read-doc-meta-dir=[ROOT]/foo/target/debug/build/dep/[HASH]/out`
+[RUNNING] `rustdoc -o [ROOT]/foo/target/doc -Zunstable-options --edition=2015 --read-doc-meta-dir=[ROOT]/foo/target/debug/build/dep/[HASH]/out`
 [FINISHED] documentation merge in [ELAPSED]s
 [GENERATED] [ROOT]/foo/target/doc/dep/index.html