diff --git a/src/cmd/go/internal/modload/init.go b/src/cmd/go/internal/modload/init.go
index f960edd251..69a3bc8bfe 100644
--- a/src/cmd/go/internal/modload/init.go
+++ b/src/cmd/go/internal/modload/init.go
@@ -993,6 +993,9 @@ func makeMainModules(ms []module.Version, rootDirs []string, modFiles []*modfile
 	}
 	mainModulePaths := make(map[string]bool)
 	for _, m := range ms {
+		if mainModulePaths[m.Path] {
+			base.Errorf("go: module %s appears multiple times in workspace", m.Path)
+		}
 		mainModulePaths[m.Path] = true
 	}
 	replacedByWorkFile := make(map[string]bool)
diff --git a/src/cmd/go/testdata/script/work_issue54048.txt b/src/cmd/go/testdata/script/work_issue54048.txt
new file mode 100644
index 0000000000..ced3d9074a
--- /dev/null
+++ b/src/cmd/go/testdata/script/work_issue54048.txt
@@ -0,0 +1,19 @@
+! go list -m -json all
+stderr 'go: module example.com/foo appears multiple times in workspace'
+
+-- go.work --
+go 1.18
+
+use (
+        ./a
+        ./b
+)
+-- a/go.mod --
+module example.com/foo
+
+go 1.18
+
+-- b/go.mod --
+module example.com/foo
+
+go 1.18
diff --git a/src/cmd/go/testdata/script/work_sum_mismatch.txt b/src/cmd/go/testdata/script/work_sum_mismatch.txt
index 9e9474304e..ca5d71dc5e 100644
--- a/src/cmd/go/testdata/script/work_sum_mismatch.txt
+++ b/src/cmd/go/testdata/script/work_sum_mismatch.txt
@@ -42,7 +42,7 @@ func main() {
 -- b/go.mod --
 go 1.18
 
-module example.com/hi
+module example.com/hi2
 
 require "rsc.io/quote" v1.5.2
 -- b/go.sum --