diff --git a/poi/src/main/java/org/apache/poi/poifs/crypt/agile/AgileEncryptionInfoBuilder.java b/poi/src/main/java/org/apache/poi/poifs/crypt/agile/AgileEncryptionInfoBuilder.java
index 0674305b22..dabc789e8a 100644
--- a/poi/src/main/java/org/apache/poi/poifs/crypt/agile/AgileEncryptionInfoBuilder.java
+++ b/poi/src/main/java/org/apache/poi/poifs/crypt/agile/AgileEncryptionInfoBuilder.java
@@ -36,6 +36,10 @@ public class AgileEncryptionInfoBuilder implements EncryptionInfoBuilder {
 
     @Override
     public void initialize(EncryptionInfo info, LittleEndianInput dis) throws IOException {
+        if (!(dis instanceof InputStream)) {
+            throw new IllegalArgumentException("Had unexpected type of input: " + (dis == null ? "<null>" : dis.getClass()));
+        }
+
         EncryptionDocument ed = parseDescriptor((InputStream)dis);
         info.setHeader(new AgileEncryptionHeader(ed));
         info.setVerifier(new AgileEncryptionVerifier(ed));
diff --git a/poi/src/test/java/org/apache/poi/hssf/dev/BaseTestIteratingXLS.java b/poi/src/test/java/org/apache/poi/hssf/dev/BaseTestIteratingXLS.java
index 6e18940a72..b239be7923 100644
--- a/poi/src/test/java/org/apache/poi/hssf/dev/BaseTestIteratingXLS.java
+++ b/poi/src/test/java/org/apache/poi/hssf/dev/BaseTestIteratingXLS.java
@@ -89,6 +89,7 @@ public abstract class BaseTestIteratingXLS {
         // fuzzed binaries
         excludes.put("clusterfuzz-testcase-minimized-POIHSSFFuzzer-6322470200934400.xls", RuntimeException.class);
         excludes.put("clusterfuzz-testcase-minimized-POIHSSFFuzzer-4819588401201152.xls", RuntimeException.class);
+        excludes.put("clusterfuzz-testcase-minimized-POIHSSFFuzzer-6537773940867072.xls", RuntimeException.class);
         return excludes;
     }
 
diff --git a/test-data/spreadsheet/clusterfuzz-testcase-minimized-POIHSSFFuzzer-6537773940867072.xls b/test-data/spreadsheet/clusterfuzz-testcase-minimized-POIHSSFFuzzer-6537773940867072.xls
new file mode 100644
index 0000000000..646cf0d46a
Binary files /dev/null and b/test-data/spreadsheet/clusterfuzz-testcase-minimized-POIHSSFFuzzer-6537773940867072.xls differ
diff --git a/test-data/spreadsheet/stress.xls b/test-data/spreadsheet/stress.xls
index 4a146faa1f..26af0e5ba3 100644
Binary files a/test-data/spreadsheet/stress.xls and b/test-data/spreadsheet/stress.xls differ