diff --git a/decode.c b/decode.c
index a6bac57..4c300cb 100644
--- a/decode.c
+++ b/decode.c
@@ -560,6 +560,16 @@ prefix_end:
         }
     }
 
+    if (UNLIKELY(instr->type == FDI_3DNOW))
+    {
+        unsigned opc3dn = instr->imm;
+        if (opc3dn & 0x40)
+            return FD_ERR_UD;
+        uint64_t msk = opc3dn & 0x80 ? 0x88d144d144d14400 : 0x30003000;
+        if (!(msk >> (opc3dn & 0x3f) & 1))
+            return FD_ERR_UD;
+    }
+
     if (UNLIKELY(prefix_lock)) {
         if (!DESC_LOCK(desc) || instr->operands[0].type != FD_OT_MEM)
             return FD_ERR_UD;
diff --git a/tests/test_decode.c b/tests/test_decode.c
index ef95550..6712861 100644
--- a/tests/test_decode.c
+++ b/tests/test_decode.c
@@ -509,6 +509,20 @@ main(int argc, char** argv)
     TEST32("\xd9\x20", "fldenv [eax]");
     TEST64("\xd9\x20", "fldenv [rax]");
 
+    // 3DNow!
+    TEST("\x0f\x0f\xc0\x00", "UD");
+    TEST("\x0f\x0f\xc0\x0c", "3dnow mm0, mm0, 0xc"); // PI2FW
+    TEST("\x0f\x0f\xc0\x0d", "3dnow mm0, mm0, 0xd"); // PI2FD
+    TEST("\x0f\x0f\xc0\x0e", "UD");
+    TEST("\x0f\x0f\xc0\x1c", "3dnow mm0, mm0, 0x1c"); // PF2IW
+    TEST("\x0f\x0f\xc0\x1d", "3dnow mm0, mm0, 0x1d"); // PF2ID
+    TEST("\x0f\x0f\xc0\x42", "UD");
+    TEST("\x0f\x0f\xc0\x80", "UD");
+    TEST("\x0f\x0f\xc0\x8a", "3dnow mm0, mm0, 0x8a"); // PFNACC
+    TEST("\x0f\x0f\xc0\xa0", "3dnow mm0, mm0, 0xa0"); // PFCMPGT
+    TEST("\x0f\x0f\xc0\xb6", "3dnow mm0, mm0, 0xb6"); // PFRCPIT2
+    TEST("\x0f\x0f\xc0\xbf", "3dnow mm0, mm0, 0xbf"); // PAVGUSB
+
     puts(failed ? "Some tests FAILED" : "All tests PASSED");
     return failed ? EXIT_FAILURE : EXIT_SUCCESS;
 }