diff --git a/src/test/shell/bazel/python_version_test.sh b/src/test/shell/bazel/python_version_test.sh
index 096f7d163922ee..a01977a8798ea8 100755
--- a/src/test/shell/bazel/python_version_test.sh
+++ b/src/test/shell/bazel/python_version_test.sh
@@ -52,18 +52,12 @@ case "$(uname -s | tr [:upper:] [:lower:])" in
 msys*)
   # As of 2018-08-14, Bazel on Windows only supports MSYS Bash.
   declare -r is_windows=true
-  # As of 2019-04-26, this test is disabled on Windows (via "no_windows" tag),
+  # As of 2019-05-18, this test is disabled on Windows (via "no_windows" tag),
   # so this code shouldn't even have run.
-  # TODO(bazelbuild/continuous-integration#578): Enable this test for Windows.
+  # TODO(#7844): Enable this test for Windows once our autodetecting toolchain
+  # works transparently for this platform.
   fail "This test does not run on Windows."
   ;;
-darwin*)
-  # As of 2019-04-26, this test is disabled on mac, but there's no "no_mac" tag
-  # so we just have to trivially succeed.
-  # TODO(bazelbuild/continuous-integration#578): Enable this test for Mac.
-  echo "This test does not run on Mac; exiting early." >&2
-  exit 0
-  ;;
 *)
   declare -r is_windows=false
   ;;
@@ -654,4 +648,58 @@ configuration, which uses Python 3"
   expect_not_log "program that was built in the host configuration"
 }
 
+# Regression test for (bazelbuild/continuous-integration#578): Ensure that a
+# py_binary built with the autodetecting toolchain works when used as a tool
+# from Starlark rule. In particular, the wrapper script that launches the real
+# second-stage interpreter must be able to tolerate PATH not being set.
+function test_py_binary_with_autodetecting_toolchain_usable_as_tool() {
+  mkdir -p test
+
+  cat > test/BUILD << 'EOF'
+load(":tooluser.bzl", "tooluser_rule")
+
+py_binary(
+    name = "tool",
+    srcs = ["tool.py"],
+)
+
+tooluser_rule(
+    name = "tooluser",
+    out = "out.txt",
+)
+EOF
+  cat > test/tooluser.bzl << EOF
+def _tooluser_rule_impl(ctx):
+    ctx.actions.run(
+        inputs = [],
+        outputs = [ctx.outputs.out],
+        executable = ctx.executable._tool,
+        arguments = [ctx.outputs.out.path],
+    )
+
+tooluser_rule = rule(
+    implementation = _tooluser_rule_impl,
+    attrs = {
+        "_tool": attr.label(
+            executable = True,
+            default = "//test:tool",
+            # cfg param is required but its value doesn't matter
+            cfg = "target"),
+        "out": attr.output(),
+    },
+)
+EOF
+  cat > test/tool.py << EOF
+import sys
+with open(sys.argv[1], 'wt') as out:
+    print("Tool output", file=out)
+EOF
+
+  bazel build //test:tooluser \
+      --incompatible_use_python_toolchains=true \
+      || fail "bazel build failed"
+  cat bazel-bin/test/out.txt &> $TEST_log
+  expect_log "Tool output"
+}
+
 run_suite "Tests for how the Python rules handle Python 2 vs Python 3"
diff --git a/tools/python/pywrapper_template.txt b/tools/python/pywrapper_template.txt
index 5153ca51a97aa8..f4dbd02618c975 100644
--- a/tools/python/pywrapper_template.txt
+++ b/tools/python/pywrapper_template.txt
@@ -15,6 +15,13 @@ die() {
     exit 1
 }
 
+# Make sure PATH is exported. If we're called with PATH unset, as happens when
+# we're invoked as a tool during the build, the shell will initialize its own
+# PATH but not necessarily export it. This would break our call to `which`. See
+# https://github.com/bazelbuild/continuous-integration/issues/578 for more
+# information.
+export PATH
+
 # Try the "python%VERSION%" command name first, then fall back on "python".
 PYTHON_BIN=`which python%VERSION% || echo ""`
 USED_FALLBACK=0