diff --git a/share/man/man4/ddb.4 b/share/man/man4/ddb.4
index cb883216f91..6b072ba1ee3 100644
--- a/share/man/man4/ddb.4
+++ b/share/man/man4/ddb.4
@@ -264,7 +264,9 @@ The location is also displayed in hex at the beginning of each line.
 display as an instruction
 .It Cm I
 display as an instruction with possible alternate formats depending on the
-machine, but none of the supported architectures have an alternate format
+machine.
+On i386, this selects the alternate format for the instruction decoding
+(16 bits in a 32-bit code segment and vice versa).
 .It Cm S
 display a symbol name for the pointer stored at the address
 .El
diff --git a/sys/ddb/db_examine.c b/sys/ddb/db_examine.c
index de2bbe4e773..a1e5a2858ab 100644
--- a/sys/ddb/db_examine.c
+++ b/sys/ddb/db_examine.c
@@ -241,7 +241,7 @@ db_print_loc_and_inst(db_addr_t loc)
 	db_printsym(loc, DB_STGY_PROC);
 	if (db_search_symbol(loc, DB_STGY_PROC, &off) != C_DB_SYM_NULL) {
 		db_printf(":\t");
-		(void)db_disasm(loc, true);
+		(void)db_disasm(loc, false);
 	}
 }
 
diff --git a/sys/i386/i386/db_disasm.c b/sys/i386/i386/db_disasm.c
index 2b398da8e96..5728fe5def0 100644
--- a/sys/i386/i386/db_disasm.c
+++ b/sys/i386/i386/db_disasm.c
@@ -31,6 +31,7 @@ __FBSDID("$FreeBSD$");
  * Instruction disassembler.
  */
 #include <sys/param.h>
+#include <sys/kdb.h>
 
 #include <ddb/ddb.h>
 #include <ddb/db_access.h>
@@ -1168,9 +1169,17 @@ db_disasm(db_addr_t loc, bool altfmt)
 	int	len;
 	struct i_addr	address;
 
+	if (db_segsize(kdb_frame) == 16)
+	   altfmt = !altfmt;
 	get_value_inc(inst, loc, 1, FALSE);
-	short_addr = FALSE;
-	size = LONG;
+	if (altfmt) {
+	    short_addr = TRUE;
+	    size = WORD;
+	}
+	else {
+	    short_addr = FALSE;
+	    size = LONG;
+	}
 	seg = NULL;
 
 	/*
diff --git a/sys/i386/i386/db_interface.c b/sys/i386/i386/db_interface.c
index 7079e5688b8..3c0ac813ff6 100644
--- a/sys/i386/i386/db_interface.c
+++ b/sys/i386/i386/db_interface.c
@@ -135,6 +135,30 @@ db_write_bytes(vm_offset_t addr, size_t size, char *data)
 	return (ret);
 }
 
+int
+db_segsize(struct trapframe *tfp)
+{
+	struct proc_ldt *plp;
+	struct segment_descriptor *sdp;
+	int sel;
+
+	if (tfp == NULL)
+	    return (32);
+	if (tfp->tf_eflags & PSL_VM)
+	    return (16);
+	sel = tfp->tf_cs & 0xffff;
+	if (sel == GSEL(GCODE_SEL, SEL_KPL))
+	    return (32);
+	/* Rare cases follow.  User mode cases are currently unreachable. */
+	if (ISLDT(sel)) {
+	    plp = curthread->td_proc->p_md.md_ldt;
+	    sdp = (plp != NULL) ? &plp->ldt_sd : &ldt[0].sd;
+	} else {
+	    sdp = &gdt[PCPU_GET(cpuid) * NGDT].sd;
+	}
+	return (sdp[IDXSEL(sel)].sd_def32 == 0 ? 16 : 32);
+}
+
 void
 db_show_mdpcpu(struct pcpu *pc)
 {
diff --git a/sys/i386/i386/db_trace.c b/sys/i386/i386/db_trace.c
index 4918ed232dd..4f5f4130f2a 100644
--- a/sys/i386/i386/db_trace.c
+++ b/sys/i386/i386/db_trace.c
@@ -421,6 +421,17 @@ db_backtrace(struct thread *td, struct trapframe *tf, struct i386_frame *frame,
 	int instr, narg;
 	boolean_t first;
 
+	if (db_segsize(tf) == 16) {
+		db_printf(
+"--- 16-bit%s, cs:eip = %#x:%#x, ss:esp = %#x:%#x, ebp = %#x, tf = %p ---\n",
+		    (tf->tf_eflags & PSL_VM) ? " (vm86)" : "",
+		    tf->tf_cs, tf->tf_eip,
+		    TF_HAS_STACKREGS(tf) ? tf->tf_ss : rss(),
+		    TF_HAS_STACKREGS(tf) ? tf->tf_esp : (intptr_t)&tf->tf_esp,
+		    tf->tf_ebp, tf);
+		return (0);
+	}
+
 	/*
 	 * If an indirect call via an invalid pointer caused a trap,
 	 * %pc contains the invalid address while the return address
diff --git a/sys/i386/include/db_machdep.h b/sys/i386/include/db_machdep.h
index 3ab06486a3f..e8d1d8eab95 100644
--- a/sys/i386/include/db_machdep.h
+++ b/sys/i386/include/db_machdep.h
@@ -98,4 +98,6 @@ do {						\
 #define	DB_SMALL_VALUE_MAX	0x7fffffff
 #define	DB_SMALL_VALUE_MIN	(-0x400001)
 
+int	db_segsize(struct trapframe *tfp);
+
 #endif /* !_MACHINE_DB_MACHDEP_H_ */