diff --git a/docs/flatten.md b/docs/flatten.md
index 08903691e4..525991d413 100644
--- a/docs/flatten.md
+++ b/docs/flatten.md
@@ -1167,7 +1167,7 @@ See @rules_rust//rust:repositories.bzl for examples of defining the @rust_cpuX r
| default_edition | The edition to use for rust_* rules that don't specify an edition. | String | optional | "2018" |
| dylib_ext | The extension for dynamic libraries created from rustc. | String | required | |
| exec_triple | The platform triple for the toolchains execution environment. For more details see: https://docs.bazel.build/versions/master/skylark/rules.html#configurations | String | optional | "" |
-| opt_level | Rustc optimization levels. | Dictionary: String -> String | optional | {"dbg": "0", "fastbuild": "0", "opt": "3"} |
+| opt_level | Rustc optimization levels. | Dictionary: String -> String | optional | {"dbg": "0", "fastbuild": "1", "opt": "3"} |
| os | The operating system for the current toolchain | String | required | |
| rust_doc | The location of the rustdoc
binary. Can be a direct source or a filegroup containing one item. | Label | optional | None |
| rust_lib | The rust standard library. | Label | optional | None |
diff --git a/docs/rust_repositories.md b/docs/rust_repositories.md
index b7374ee4b5..50cc8c6d8e 100644
--- a/docs/rust_repositories.md
+++ b/docs/rust_repositories.md
@@ -93,7 +93,7 @@ See @rules_rust//rust:repositories.bzl for examples of defining the @rust_cpuX r
| default_edition | The edition to use for rust_* rules that don't specify an edition. | String | optional | "2018" |
| dylib_ext | The extension for dynamic libraries created from rustc. | String | required | |
| exec_triple | The platform triple for the toolchains execution environment. For more details see: https://docs.bazel.build/versions/master/skylark/rules.html#configurations | String | optional | "" |
-| opt_level | Rustc optimization levels. | Dictionary: String -> String | optional | {"dbg": "0", "fastbuild": "0", "opt": "3"} |
+| opt_level | Rustc optimization levels. | Dictionary: String -> String | optional | {"dbg": "0", "fastbuild": "1", "opt": "3"} |
| os | The operating system for the current toolchain | String | required | |
| rust_doc | The location of the rustdoc
binary. Can be a direct source or a filegroup containing one item. | Label | optional | None |
| rust_lib | The rust standard library. | Label | optional | None |
diff --git a/rust/toolchain.bzl b/rust/toolchain.bzl
index 834382ecf3..b9b02cf639 100644
--- a/rust/toolchain.bzl
+++ b/rust/toolchain.bzl
@@ -342,7 +342,7 @@ rust_toolchain = rule(
doc = "Rustc optimization levels.",
default = {
"dbg": "0",
- "fastbuild": "0",
+ "fastbuild": "1",
"opt": "3",
},
),