diff --git a/main.go b/main.go
index 4ba8cbe..5396fa4 100644
--- a/main.go
+++ b/main.go
@@ -2058,7 +2058,7 @@ To install Go, see: https://go.dev/doc/install
 		return errJustExit(1)
 	}
 	if err := json.Unmarshal(out, &cache.GoEnv); err != nil {
-		return err
+		return fmt.Errorf(`cannot unmarshal from "go env -json": %w`, err)
 	}
 	cache.GOGARBLE = os.Getenv("GOGARBLE")
 	if cache.GOGARBLE != "" {
diff --git a/shared.go b/shared.go
index d3c3ab5..578ee0f 100644
--- a/shared.go
+++ b/shared.go
@@ -64,14 +64,14 @@ func loadSharedCache() error {
 	startTime := time.Now()
 	f, err := os.Open(filepath.Join(sharedTempDir, "main-cache.gob"))
 	if err != nil {
-		return fmt.Errorf(`cannot open shared file, this is most likely due to not running "garble [command]"`)
+		return fmt.Errorf(`cannot open shared file: %v; did you run "garble [command]"?`, err)
 	}
 	defer func() {
 		debugf("shared cache loaded in %s from %s", debugSince(startTime), f.Name())
 	}()
 	defer f.Close()
 	if err := gob.NewDecoder(f).Decode(&cache); err != nil {
-		return err
+		return fmt.Errorf("cannot decode shared file: %v", err)
 	}
 	return nil
 }
diff --git a/testdata/scripts/basic.txt b/testdata/scripts/basic.txt
index cec5446..c6ec453 100644
--- a/testdata/scripts/basic.txt
+++ b/testdata/scripts/basic.txt
@@ -29,7 +29,7 @@ stdout 'unknown'
 
 # Check that we fail if the user used "go build -toolexec garble" instead of "garble build"
 ! go build -toolexec=garble -o=main$exe garble_main.go
-stderr 'not running "garble \[command\]"'
+stderr 'run "garble \[command\]"'
 
 # Also check that the binary is reproducible.
 # No packages should be rebuilt either, thanks to the build cache.
diff --git a/testdata/scripts/help.txt b/testdata/scripts/help.txt
index 884dcf2..bd819ab 100644
--- a/testdata/scripts/help.txt
+++ b/testdata/scripts/help.txt
@@ -75,7 +75,7 @@ stderr 'must precede command, like: garble -seed=random build \./pkg'
 
 [!windows] ! garble /does/not/exist/compile
 [windows] ! garble C:\does\not\exist\compile
-stderr 'not running "garble \[command\]"'
+stderr 'run "garble \[command\]"'
 
 # Test the version command. Note that test binaries exclude VCS build info,
 # and we reuse the test binary for garble itself, so that's missing.