diff --git a/target/hexagon/decode.c b/target/hexagon/decode.c
index 041c8de751..946c55cc71 100644
--- a/target/hexagon/decode.c
+++ b/target/hexagon/decode.c
@@ -1,5 +1,5 @@
 /*
- *  Copyright(c) 2019-2022 Qualcomm Innovation Center, Inc. All Rights Reserved.
+ *  Copyright(c) 2019-2023 Qualcomm Innovation Center, Inc. All Rights Reserved.
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -797,7 +797,26 @@ static bool decode_parsebits_is_loopend(uint32_t encoding32)
     return bits == 0x2;
 }
 
-static void
+static bool has_valid_slot_assignment(Packet *pkt)
+{
+    int used_slots = 0;
+    for (int i = 0; i < pkt->num_insns; i++) {
+        int slot_mask;
+        Insn *insn = &pkt->insn[i];
+        if (decode_opcode_ends_loop(insn->opcode)) {
+            /* We overload slot 0 for endloop. */
+            continue;
+        }
+        slot_mask = 1 << insn->slot;
+        if (used_slots & slot_mask) {
+            return false;
+        }
+        used_slots |= slot_mask;
+    }
+    return true;
+}
+
+static bool
 decode_set_slot_number(Packet *pkt)
 {
     int slot;
@@ -886,6 +905,8 @@ decode_set_slot_number(Packet *pkt)
         /* Then push it to slot0 */
         pkt->insn[slot1_iidx].slot = 0;
     }
+
+    return has_valid_slot_assignment(pkt);
 }
 
 /*
@@ -961,8 +982,11 @@ int decode_packet(int max_words, const uint32_t *words, Packet *pkt,
     decode_apply_extenders(pkt);
     if (!disas_only) {
         decode_remove_extenders(pkt);
+        if (!decode_set_slot_number(pkt)) {
+            /* Invalid packet */
+            return 0;
+        }
     }
-    decode_set_slot_number(pkt);
     decode_fill_newvalue_regno(pkt);
 
     if (pkt->pkt_has_hvx) {
diff --git a/tests/tcg/hexagon/Makefile.target b/tests/tcg/hexagon/Makefile.target
index 6109a7ed10..890cceed5d 100644
--- a/tests/tcg/hexagon/Makefile.target
+++ b/tests/tcg/hexagon/Makefile.target
@@ -50,6 +50,13 @@ HEX_TESTS += vector_add_int
 HEX_TESTS += scatter_gather
 HEX_TESTS += hvx_misc
 HEX_TESTS += hvx_histogram
+HEX_TESTS += invalid-slots
+
+run-and-check-exception = $(call run-test,$2,$3 2>$2.stderr; \
+	test $$? -eq 1 && grep -q "exception $(strip $1)" $2.stderr)
+
+run-invalid-slots: invalid-slots
+	$(call run-and-check-exception, 0x15, $@, $(QEMU) $(QEMU_OPTS) $<)
 
 HEX_TESTS += test_abs
 HEX_TESTS += test_bitcnt
diff --git a/tests/tcg/hexagon/invalid-slots.c b/tests/tcg/hexagon/invalid-slots.c
new file mode 100644
index 0000000000..366ce4f42f
--- /dev/null
+++ b/tests/tcg/hexagon/invalid-slots.c
@@ -0,0 +1,29 @@
+/*
+ *  Copyright(c) 2023 Qualcomm Innovation Center, Inc. All Rights Reserved.
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+char mem[8] __attribute__((aligned(8)));
+
+int main()
+{
+    asm volatile(
+        "r0 = #mem\n"
+        /* Invalid packet (2 instructions at slot 0): */
+        ".word 0xa1804100\n" /* { memw(r0) = r1;      */
+        ".word 0x28032804\n" /*   r3 = #0; r4 = #0 }  */
+        : : : "r0", "r3", "r4", "memory");
+    return 0;
+}