diff --git a/lib/zlib_dfltcc/dfltcc.h b/lib/zlib_dfltcc/dfltcc.h
index b96232bdd44d..0f2a16d7a48a 100644
--- a/lib/zlib_dfltcc/dfltcc.h
+++ b/lib/zlib_dfltcc/dfltcc.h
@@ -80,6 +80,7 @@ struct dfltcc_param_v0 {
     uint8_t csb[1152];
 };
 
+static_assert(offsetof(struct dfltcc_param_v0, csb) == 384);
 static_assert(sizeof(struct dfltcc_param_v0) == 1536);
 
 #define CVT_CRC32 0
diff --git a/lib/zlib_dfltcc/dfltcc_util.h b/lib/zlib_dfltcc/dfltcc_util.h
index 4a46b5009f0d..10509270d822 100644
--- a/lib/zlib_dfltcc/dfltcc_util.h
+++ b/lib/zlib_dfltcc/dfltcc_util.h
@@ -2,6 +2,8 @@
 #ifndef DFLTCC_UTIL_H
 #define DFLTCC_UTIL_H
 
+#include "dfltcc.h"
+#include <linux/kmsan-checks.h>
 #include <linux/zutil.h>
 
 /*
@@ -20,6 +22,7 @@ typedef enum {
 #define DFLTCC_CMPR 2
 #define DFLTCC_XPND 4
 #define HBT_CIRCULAR (1 << 7)
+#define DFLTCC_FN_MASK ((1 << 7) - 1)
 #define HB_BITS 15
 #define HB_SIZE (1 << HB_BITS)
 
@@ -34,6 +37,7 @@ static inline dfltcc_cc dfltcc(
 )
 {
     Byte *t2 = op1 ? *op1 : NULL;
+    unsigned char *orig_t2 = t2;
     size_t t3 = len1 ? *len1 : 0;
     const Byte *t4 = op2 ? *op2 : NULL;
     size_t t5 = len2 ? *len2 : 0;
@@ -59,6 +63,30 @@ static inline dfltcc_cc dfltcc(
                      : "cc", "memory");
     t2 = r2; t3 = r3; t4 = r4; t5 = r5;
 
+    /*
+     * Unpoison the parameter block and the output buffer.
+     * This is a no-op in non-KMSAN builds.
+     */
+    switch (fn & DFLTCC_FN_MASK) {
+    case DFLTCC_QAF:
+        kmsan_unpoison_memory(param, sizeof(struct dfltcc_qaf_param));
+        break;
+    case DFLTCC_GDHT:
+        kmsan_unpoison_memory(param, offsetof(struct dfltcc_param_v0, csb));
+        break;
+    case DFLTCC_CMPR:
+        kmsan_unpoison_memory(param, sizeof(struct dfltcc_param_v0));
+        kmsan_unpoison_memory(
+                orig_t2,
+                t2 - orig_t2 +
+                    (((struct dfltcc_param_v0 *)param)->sbb == 0 ? 0 : 1));
+        break;
+    case DFLTCC_XPND:
+        kmsan_unpoison_memory(param, sizeof(struct dfltcc_param_v0));
+        kmsan_unpoison_memory(orig_t2, t2 - orig_t2);
+        break;
+    }
+
     if (op1)
         *op1 = t2;
     if (len1)