diff --git a/src/util/fipstools/acvp/acvptool/acvp.go b/src/util/fipstools/acvp/acvptool/acvp.go
index e92424b77..cbb07f63d 100644
--- a/src/util/fipstools/acvp/acvptool/acvp.go
+++ b/src/util/fipstools/acvp/acvptool/acvp.go
@@ -598,14 +598,14 @@ func main() {
 		}
 		os.Stdout.Write(regcapBytes)
 		os.Stdout.WriteString("\n")
-		os.Exit(0)
+		return
 	}
 
 	if len(*jsonInputFile) > 0 {
 		if err := processFile(*jsonInputFile, supportedAlgos, middle); err != nil {
 			log.Fatalf("failed to process input file: %s", err)
 		}
-		os.Exit(0)
+		return
 	}
 
 	var requestedAlgosFlag string
@@ -789,7 +789,7 @@ func main() {
 
 	if len(*fetchFlag) > 0 {
 		io.WriteString(fetchOutputTee, "]\n")
-		os.Exit(0)
+		return
 	}
 
 	if ok, err := getResultsWithRetry(server, url); err != nil {
diff --git a/src/util/fipstools/acvp/acvptool/subprocess/subprocess.go b/src/util/fipstools/acvp/acvptool/subprocess/subprocess.go
index 9167b4720..f1cb5fa88 100644
--- a/src/util/fipstools/acvp/acvptool/subprocess/subprocess.go
+++ b/src/util/fipstools/acvp/acvptool/subprocess/subprocess.go
@@ -48,8 +48,6 @@ type Subprocess struct {
 	pendingReads chan pendingRead
 	// readerFinished is a channel that is closed if `readerRoutine` has finished (e.g. because of a read error).
 	readerFinished chan struct{}
-	// readerError is set iff readerFinished is closed. If non-nil then it is the read error that caused `readerRoutine` to finished.
-	readerError error
 }
 
 // pendingRead represents an expected response from the modulewrapper.
@@ -153,6 +151,7 @@ func (m *Subprocess) Close() {
 	m.stdout.Close()
 	m.stdin.Close()
 	m.cmd.Wait()
+	close(m.pendingReads)
 	<-m.readerFinished
 }
 
@@ -176,7 +175,7 @@ func (m *Subprocess) flush() error {
 func (m *Subprocess) enqueueRead(pending pendingRead) error {
 	select {
 	case <-m.readerFinished:
-		return m.readerError
+		panic("attempted to enqueue request after the reader failed")
 	default:
 	}
 
@@ -266,7 +265,7 @@ func (m *Subprocess) Transact(cmd string, expectedNumResults int, args ...[]byte
 	case <-done:
 		return result, nil
 	case <-m.readerFinished:
-		return nil, m.readerError
+		panic("was still waiting for a result when the reader finished")
 	}
 }
 
@@ -284,13 +283,11 @@ func (m *Subprocess) readerRoutine() {
 
 		result, err := m.readResult(pendingRead.cmd, pendingRead.expectedNumResults)
 		if err != nil {
-			m.readerError = err
-			return
+			panic(fmt.Errorf("failed to read from subprocess: %w", err))
 		}
 
 		if err := pendingRead.callback(result); err != nil {
-			m.readerError = err
-			return
+			panic(fmt.Errorf("result from subprocess was rejected: %w", err))
 		}
 	}
 }