diff --git a/external-sop/src/main/java/sop/external/operation/DetachedSignExternal.java b/external-sop/src/main/java/sop/external/operation/DetachedSignExternal.java
index 3e369f1..7c579d4 100644
--- a/external-sop/src/main/java/sop/external/operation/DetachedSignExternal.java
+++ b/external-sop/src/main/java/sop/external/operation/DetachedSignExternal.java
@@ -100,6 +100,9 @@ public class DetachedSignExternal implements DetachedSign {
                         processOut.close();
                     } catch (IOException e) {
                         // Ignore Stream closed
+                        if (!"Stream closed".equals(e.getMessage())) {
+                            throw e;
+                        }
                     }
 
                     while ((r = processIn.read(buf)) > 0) {