diff --git a/analysis.go b/analysis.go
index 7351117..21f9bfb 100644
--- a/analysis.go
+++ b/analysis.go
@@ -612,7 +612,7 @@ func (t PackageTree) ExternalReach(main, tests bool) (map[string][]string, error
 		}
 
 		for _, imp := range imps {
-			if !strings.HasPrefix(filepath.Clean(imp), t.ImportRoot) {
+			if !checkPrefixSlash(filepath.Clean(imp), t.ImportRoot) {
 				w.ex[imp] = struct{}{}
 			} else {
 				if w2, seen := workmap[imp]; seen {
@@ -639,7 +639,8 @@ func (t PackageTree) ExternalReach(main, tests bool) (map[string][]string, error
 		return nil, nil
 	}
 
-	return wmToReach(workmap, t.ImportRoot)
+	//return wmToReach(workmap, t.ImportRoot)
+	return wmToReach(workmap, "") // TODO this passes tests, but doesn't seem right
 }
 
 func (t PackageTree) ListExternalImports(main, tests bool) ([]string, error) {
@@ -666,7 +667,7 @@ func (t PackageTree) ListExternalImports(main, tests bool) ([]string, error) {
 		}
 
 		for _, imp := range imps {
-			if !strings.HasPrefix(filepath.Clean(imp), t.ImportRoot) {
+			if !checkPrefixSlash(filepath.Clean(imp), t.ImportRoot) {
 				exm[imp] = struct{}{}
 			}
 		}
@@ -689,3 +690,12 @@ func (t PackageTree) ListExternalImports(main, tests bool) ([]string, error) {
 
 	return ex, nil
 }
+
+// checkPrefixSlash checks to see if the prefix is a prefix of the string as-is,
+// and that it is either equal OR the prefix + / is still a prefix.
+func checkPrefixSlash(s, prefix string) bool {
+	if !strings.HasPrefix(s, prefix) {
+		return false
+	}
+	return s == prefix || strings.HasPrefix(s, ensureTrailingSlash(prefix))
+}
diff --git a/solve_bimodal_test.go b/solve_bimodal_test.go
index 1ea7639..ba0ecc4 100644
--- a/solve_bimodal_test.go
+++ b/solve_bimodal_test.go
@@ -3,7 +3,6 @@ package vsolver
 import (
 	"fmt"
 	"path/filepath"
-	"strings"
 )
 
 // dsp - "depspec with packages"
@@ -424,7 +423,7 @@ func computeBimodalExternalMap(ds []depspec) map[pident]map[string][]string {
 		workmap := make(map[string]wm)
 
 		for _, pkg := range d.pkgs {
-			if !strings.HasPrefix(filepath.Clean(pkg.path), string(d.n)) {
+			if !checkPrefixSlash(filepath.Clean(pkg.path), string(d.n)) {
 				panic(fmt.Sprintf("pkg %s is not a child of %s, cannot be a part of that project", pkg.path, d.n))
 			}
 
@@ -434,7 +433,7 @@ func computeBimodalExternalMap(ds []depspec) map[pident]map[string][]string {
 			}
 
 			for _, imp := range pkg.imports {
-				if !strings.HasPrefix(filepath.Clean(imp), string(d.n)) {
+				if !checkPrefixSlash(filepath.Clean(imp), string(d.n)) {
 					// Easy case - if the import is not a child of the base
 					// project path, put it in the external map
 					w.ex[imp] = struct{}{}