diff --git a/go/tools/bzltestutil/lcov.go b/go/tools/bzltestutil/lcov.go
index 8b94b162a3..5150ae59f6 100644
--- a/go/tools/bzltestutil/lcov.go
+++ b/go/tools/bzltestutil/lcov.go
@@ -28,6 +28,9 @@ import (
 	"testing/internal/testdeps"
 )
 
+// Lock in the COVERAGE_DIR during test setup in case the test uses e.g. os.Clearenv.
+var coverageDir = os.Getenv("COVERAGE_DIR")
+
 // ConvertCoverToLcov converts the go coverprofile file coverage.dat.cover to
 // the expectedLcov format and stores it in coverage.dat, where it is picked up by
 // Bazel.
@@ -42,8 +45,12 @@ func ConvertCoverToLcov() error {
 	}
 	defer in.Close()
 
+	if coverageDir == "" {
+		log.Printf("Not collecting coverage: COVERAGE_DIR is not set")
+		return nil
+	}
 	// All *.dat files in $COVERAGE_DIR will be merged by Bazel's lcov_merger tool.
-	out, err := os.CreateTemp(os.Getenv("COVERAGE_DIR"), "go_coverage.*.dat")
+	out, err := os.CreateTemp(coverageDir, "go_coverage.*.dat")
 	if err != nil {
 		return err
 	}
diff --git a/tests/core/coverage/lcov_coverage_test.go b/tests/core/coverage/lcov_coverage_test.go
index a46567ccc5..d882d1ee31 100644
--- a/tests/core/coverage/lcov_coverage_test.go
+++ b/tests/core/coverage/lcov_coverage_test.go
@@ -116,6 +116,7 @@ public class Tool {
 package lib_test
 
 import (
+	"os"
 	"os/exec"
 	"path/filepath"
 	"strings"
@@ -125,6 +126,8 @@ import (
 )
 
 func TestLib(t *testing.T) {
+	// Test that coverage is collected even if this variable is corrupted by a test.
+	os.Setenv("COVERAGE_DIR", "invalid")
 	if !strings.Contains(lib.HelloFromLib(false), "\n") {
 		t.Error("Expected a newline in the output")
 	}