diff --git a/instrumenter.go b/instrumenter.go
index 8fe71c9..9f2366e 100644
--- a/instrumenter.go
+++ b/instrumenter.go
@@ -11,6 +11,7 @@ import (
 	"go/token"
 	"go/types"
 	"os"
+	"path"
 	"path/filepath"
 	"reflect"
 	"runtime"
@@ -106,7 +107,7 @@ func (i *instrumenter) instrument(srcDir, singleFile, dstDir string) bool {
 			i.instrumentFile(name, file, dstDir)
 		})
 	}
-	i.writeGobcoFiles(dstDir, pkgs)
+	i.writeGobcoFiles(srcDir, dstDir, pkgs)
 	return true
 }
 
@@ -629,7 +630,7 @@ var fixedTemplate string
 //go:embed templates/gobco_no_testmain_test.go
 var noTestMainTemplate string
 
-func (i *instrumenter) writeGobcoFiles(tmpDir string, pkgs []*ast.Package) {
+func (i *instrumenter) writeGobcoFiles(srcDir, tmpDir string, pkgs []*ast.Package) {
 	pkgname := pkgs[0].Name
 	fixPkgname := func(str string) string {
 		str = strings.TrimPrefix(str, "//go:build ignore\n// +build ignore\n\n")
@@ -642,7 +643,7 @@ func (i *instrumenter) writeGobcoFiles(tmpDir string, pkgs []*ast.Package) {
 		writeFile(filepath.Join(tmpDir, "gobco_no_testmain_test.go"), fixPkgname(noTestMainTemplate))
 	}
 
-	i.writeGobcoBlackBox(pkgs, tmpDir)
+	i.writeGobcoBlackBox(pkgs, srcDir, tmpDir)
 }
 
 func (i *instrumenter) writeGobcoGo(filename, pkgname string) {
@@ -667,35 +668,80 @@ func (i *instrumenter) writeGobcoGo(filename, pkgname string) {
 	writeFile(filename, sb.String())
 }
 
+// findPackagePath returns the canonical Go import path of the package
+// located at srcDir, by combining the enclosing module path
+// (read from go.mod) with the relative directory.
+func findPackagePath(srcDir string) (string, error) {
+	moduleRoot, moduleRel, err := findInModule(srcDir)
+	if err != nil {
+		return "", err
+	}
+	if moduleRoot == "" {
+		return "", fmt.Errorf("no go.mod found for %q", srcDir)
+	}
+
+	moduleName, err := readModuleName(moduleRoot)
+	if err != nil {
+		return "", err
+	}
+
+	if moduleRel == "." {
+		return moduleName, nil
+	}
+	// Import paths always use '/' as separator,
+	// while moduleRel uses the OS separator.
+	return path.Join(moduleName, filepath.ToSlash(moduleRel)), nil
+}
+
+// readModuleName parses the 'module' directive from go.mod in moduleRoot.
+//
+// Reading go.mod directly avoids depending on the 'go' command at instrumentation time
+// and on any external module like golang.org/x/mod.
+func readModuleName(moduleRoot string) (string, error) {
+	data, err := os.ReadFile(filepath.Join(moduleRoot, "go.mod"))
+	if err != nil {
+		return "", err
+	}
+
+	for _, line := range strings.Split(string(data), "\n") {
+		trimmed := strings.TrimSpace(line)
+		if !strings.HasPrefix(trimmed, "module") {
+			continue
+		}
+		rest := strings.TrimSpace(trimmed[len("module"):])
+		if rest == "" {
+			continue
+		}
+		// The module path may optionally be quoted.
+		if rest[0] == '"' || rest[0] == '`' {
+			unquoted, err := strconv.Unquote(rest)
+			if err != nil {
+				return "", fmt.Errorf("parsing module directive: %w", err)
+			}
+			return unquoted, nil
+		}
+		// Strip any inline comment.
+		if idx := strings.Index(rest, "//"); idx >= 0 {
+			rest = strings.TrimSpace(rest[:idx])
+		}
+		return rest, nil
+	}
+
+	return "", fmt.Errorf("no module directive in %s", filepath.Join(moduleRoot, "go.mod"))
+}
+
 // writeGobcoBlackBox makes the function 'GobcoCover' available
 // to black box tests (those in 'package x_test' instead of 'package x')
 // by delegating to the function of the same name in the main package.
-func (i *instrumenter) writeGobcoBlackBox(pkgs []*ast.Package, dstDir string) {
+func (i *instrumenter) writeGobcoBlackBox(pkgs []*ast.Package, srcDir, dstDir string) {
 	if len(pkgs) < 2 {
 		return
 	}
 
-	// Copy the 'import' directive from one of the existing files.
-	pkgName, pkgPath := "", ""
-	for _, pkg := range pkgs {
-		forEachFile(pkg, func(name string, file *ast.File) {
-			for _, imp := range file.Imports {
-				var impName string
-				p, err := strconv.Unquote(imp.Path.Value)
-				ok(err)
-				if imp.Name != nil {
-					impName = imp.Name.Name
-				} else {
-					impName = filepath.Base(p)
-				}
-
-				if impName == pkgs[0].Name {
-					pkgName = impName
-					pkgPath = p
-				}
-			}
-		})
-	}
+	pkgPath, err := findPackagePath(srcDir)
+	ok(err)
+	// Import paths use '/', so path.Base is correct on all platforms.
+	pkgName := path.Base(pkgPath)
 
 	text := "" +
 		"package " + pkgs[0].Name + "_test\n" +
diff --git a/main.go b/main.go
index afd9bff..3bf52d0 100644
--- a/main.go
+++ b/main.go
@@ -205,26 +205,40 @@ func (g *gobco) gopaths() string {
 }
 
 func (g *gobco) findInModule(dir string) (moduleRoot, moduleRel string) {
-	absDir, err := filepath.Abs(dir)
+	moduleRoot, moduleRel, err := findInModule(dir)
 	g.check(err)
+	return moduleRoot, moduleRel
+}
+
+// findInModule searches dir and its ancestors for a go.mod file.
+// It returns the directory containing that file (moduleRoot)
+// and the relative path from moduleRoot to dir (moduleRel).
+// If no go.mod is found, both returned paths are empty.
+func findInModule(dir string) (moduleRoot, moduleRel string, err error) {
+	absDir, err := filepath.Abs(dir)
+	if err != nil {
+		return "", "", err
+	}
 
 	abs := absDir
 	for {
-		if _, err := os.Lstat(filepath.Join(abs, "go.mod")); err == nil {
-			rel, err := filepath.Rel(abs, absDir)
-			g.check(err)
+		if _, statErr := os.Lstat(filepath.Join(abs, "go.mod")); statErr == nil {
+			rel, relErr := filepath.Rel(abs, absDir)
+			if relErr != nil {
+				return "", "", relErr
+			}
 
 			root := abs
 			if rel == "." {
 				root = dir
 			}
 
-			return root, rel
+			return root, rel, nil
 		}
 
 		parent := filepath.Dir(abs)
 		if parent == abs {
-			return "", ""
+			return "", "", nil
 		}
 		abs = parent
 	}
diff --git a/main_test.go b/main_test.go
index e1a1caf..9d9189e 100644
--- a/main_test.go
+++ b/main_test.go
@@ -579,3 +579,23 @@ func Test_gobcoMain__issue38(t *testing.T) {
 	})
 	s.CheckEquals(stderr, "")
 }
+
+// Test_gobcoMain__issue33 covers the case where the target package's
+// own directory contains an import of another package with the same
+// base name (here, "iface/target"), and no '_test' file imports the
+// target package directly. The previous implementation scanned imports
+// in the directory and would pick the wrong import path, producing a
+// gobco_bridge_test.go that failed to compile.
+func Test_gobcoMain__issue33(t *testing.T) {
+	s := NewSuite(t)
+	defer s.TearDownTest()
+
+	stdout, stderr := s.RunMain(0, "gobco", "./testdata/issue33/target")
+
+	s.CheckEquals(s.GobcoLines(stdout), []string{
+		"Condition coverage: 1/2",
+		"testdata/issue33/target/target.go:6:5: " +
+			"condition \"a > 0\" was once true but never false",
+	})
+	s.CheckEquals(stderr, "")
+}
diff --git a/testdata/issue33/helper/helper.go b/testdata/issue33/helper/helper.go
new file mode 100644
index 0000000..51215d3
--- /dev/null
+++ b/testdata/issue33/helper/helper.go
@@ -0,0 +1,10 @@
+// Package helper provides an indirection used by the issue #33
+// regression test, so that no file in the target package's directory
+// directly imports the target package by its real import path.
+package helper
+
+import "github.com/rillig/gobco/testdata/issue33/target"
+
+func AddViaTarget(a, b int) int {
+	return target.New().Add(a, b)
+}
diff --git a/testdata/issue33/iface/target/iface.go b/testdata/issue33/iface/target/iface.go
new file mode 100644
index 0000000..6053de0
--- /dev/null
+++ b/testdata/issue33/iface/target/iface.go
@@ -0,0 +1,8 @@
+// Package target intentionally shares its name
+// with github.com/rillig/gobco/testdata/issue33/target,
+// to reproduce the import-resolution bug from issue #33.
+package target
+
+type Adder interface {
+	Add(a, b int) int
+}
diff --git a/testdata/issue33/target/factory.go b/testdata/issue33/target/factory.go
new file mode 100644
index 0000000..c467919
--- /dev/null
+++ b/testdata/issue33/target/factory.go
@@ -0,0 +1,11 @@
+package target
+
+// The unaliased import here has filepath.Base("iface/target") == "target",
+// which equals the current package name.
+// The old import-scanning logic in writeGobcoBlackBox mistook this
+// for the target package's own import path.
+import "github.com/rillig/gobco/testdata/issue33/iface/target"
+
+func New() target.Adder {
+	return &T{}
+}
diff --git a/testdata/issue33/target/target.go b/testdata/issue33/target/target.go
new file mode 100644
index 0000000..a532cd5
--- /dev/null
+++ b/testdata/issue33/target/target.go
@@ -0,0 +1,10 @@
+package target
+
+type T struct{}
+
+func (t *T) Add(a, b int) int {
+	if a > 0 {
+		return a + b
+	}
+	return b
+}
diff --git a/testdata/issue33/target/target_test.go b/testdata/issue33/target/target_test.go
new file mode 100644
index 0000000..89535ee
--- /dev/null
+++ b/testdata/issue33/target/target_test.go
@@ -0,0 +1,13 @@
+package target_test
+
+import (
+	"testing"
+
+	"github.com/rillig/gobco/testdata/issue33/helper"
+)
+
+func TestAdd(t *testing.T) {
+	if helper.AddViaTarget(1, 2) != 3 {
+		t.Fail()
+	}
+}