diff --git a/fsw/src/cf_cfdp.c b/fsw/src/cf_cfdp.c
index bbdebfb0..fc068d7e 100644
--- a/fsw/src/cf_cfdp.c
+++ b/fsw/src/cf_cfdp.c
@@ -632,6 +632,19 @@ int CF_CFDP_RecvPh(uint8 chan_num, CF_Logical_PduBuffer_t *ph)
 
     CF_CFDP_DecodeHeader(ph->pdec, &ph->pdu_header);
 
+    /*
+     * The "large file" flag is not supported by this implementation yet.
+     * This means file sizes and offsets will be 64 bits, so codec routines
+     * will need to be updated to understand this.  OSAL also doesn't support
+     * 64-bit file access yet.
+     */
+    if (CF_CODEC_IS_OK(ph->pdec) && ph->pdu_header.large_flag)
+    {
+        CFE_EVS_SendEvent(CF_EID_ERR_PDU_LARGE_FILE, CFE_EVS_EventType_ERROR,
+                          "CF: pdu with large file bit received (unsupported)");
+        goto err_out;
+    }
+
     if (CF_CODEC_IS_OK(ph->pdec) && ph->pdu_header.pdu_type == 0)
     {
         CF_CFDP_DecodeFileDirectiveHeader(ph->pdec, &ph->fdirective);
diff --git a/fsw/src/cf_events.h b/fsw/src/cf_events.h
index 11c20bea..bbf083d0 100644
--- a/fsw/src/cf_events.h
+++ b/fsw/src/cf_events.h
@@ -64,6 +64,7 @@
 #define CF_EID_ERR_PDU_GET_EID_SIZE    52
 #define CF_EID_ERR_PDU_GET_TSN_SIZE    53
 #define CF_EID_ERR_PDU_FD_UNSUPPORTED  54
+#define CF_EID_ERR_PDU_LARGE_FILE      55
 
 /* CF_CFDP event ids (engine) */
 #define CF_EID_ERR_CFDP_RX_DROPPED      60
diff --git a/unit-test/cf_cfdp_tests.c b/unit-test/cf_cfdp_tests.c
index 60e2d434..8039f4d3 100644
--- a/unit-test/cf_cfdp_tests.c
+++ b/unit-test/cf_cfdp_tests.c
@@ -255,6 +255,12 @@ void Test_CF_CFDP_RecvPh(void)
     CF_CODEC_SET_DONE(ph->pdec);
     UtAssert_INT32_EQ(CF_CFDP_RecvPh(UT_CFDP_CHANNEL, ph), -1);
     UT_CF_AssertEventID(CF_EID_ERR_PDU_SHORT_HEADER);
+
+    /* decode error, large file bit set */
+    UT_CFDP_SetupBasicTestState(UT_CF_Setup_RX, &ph, NULL, NULL, NULL, NULL);
+    ph->pdu_header.large_flag = true;
+    UtAssert_INT32_EQ(CF_CFDP_RecvPh(UT_CFDP_CHANNEL, ph), -1);
+    UT_CF_AssertEventID(CF_EID_ERR_PDU_LARGE_FILE);
 }
 
 void Test_CF_CFDP_RecvMd(void)