diff --git a/selfhost/cmd/w6c/main.combined.ww b/selfhost/cmd/w6c/main.combined.ww
index b7287d89..4dbea470 100644
--- a/selfhost/cmd/w6c/main.combined.ww
+++ b/selfhost/cmd/w6c/main.combined.ww
@@ -24299,7 +24299,30 @@ fn cgassign(c: *cgen, n: *node) void = {
 													return;
 												};};
 											};
+											if (n.op != tkind.TK_ASSIGN) {
+												// Compound on direct struct-local
+												// scalar field: load current → push
+												// → eval rhs → combine → store
+												// (mirror cgen.c:3477 local arm).
+												let lop: str = fieldloadop(c, fi);
+												emitline("\t");
+												emitline(lop);
+												emitline("\t");
+												emitoff((lc.off + fi.foff): i64);
+												emitline("(BP), BX\n");
+												emitline("\tPUSHQ\tBX\n");
+											};
 											cgexpr(c, n.rhs);
+											if (n.op != tkind.TK_ASSIGN) {
+												emitline("\tPOPQ\tBX\n");
+												// PLUSEQ commutes; MINUSEQ needs
+												// lhs-rhs (BX old lhs, AX rhs).
+												if (n.op == tkind.TK_PLUSEQ)  { emitline("\tADDQ\tBX, AX\n"); };
+												if (n.op == tkind.TK_MINUSEQ) {
+													emitline("\tSUBQ\tAX, BX\n");
+													emitline("\tMOVQ\tBX, AX\n");
+												};
+											};
 											// str/slice field direct: str IS []u8, so both store the
 											// full 3-word {ptr,len,cap} from (AX,BX,CX) at +0/+8/+16.
 											// BP base, no scratch reload needed; the generic fldstoreop
@@ -24392,6 +24415,26 @@ fn cgassign(c: *cgen, n: *node) void = {
 										return;
 									};
 								};
+								if (n.op != tkind.TK_ASSIGN) {
+									// Compound on local `str|slice` pseudo-field:
+									// load current → push → eval rhs → combine →
+									// store (mirror cgen.c:3235 local arm).
+									emitline("\tMOVQ\t");
+									emitoff((lc.off + delta): i64);
+									emitline("(BP), BX\n");
+									emitline("\tPUSHQ\tBX\n");
+									cgexpr(c, n.rhs);
+									emitline("\tPOPQ\tBX\n");
+									if (n.op == tkind.TK_PLUSEQ)  { emitline("\tADDQ\tBX, AX\n"); };
+									if (n.op == tkind.TK_MINUSEQ) {
+										emitline("\tSUBQ\tAX, BX\n");
+										emitline("\tMOVQ\tBX, AX\n");
+									};
+									emitline("\tMOVQ\tAX, ");
+									emitoff((lc.off + delta): i64);
+									emitline("(BP)\n");
+									return;
+								};
 								cgexpr(c, n.rhs);
 								emitline("\tMOVQ\tAX, ");
 								emitoff((lc.off + delta): i64);
diff --git a/selfhost/cmd/wcc/cgenexpr.ww b/selfhost/cmd/wcc/cgenexpr.ww
index 47defe5f..1682e146 100644
--- a/selfhost/cmd/wcc/cgenexpr.ww
+++ b/selfhost/cmd/wcc/cgenexpr.ww
@@ -5658,7 +5658,30 @@ fn cgassign(c: *cgen, n: *node) void = {
 													return;
 												};};
 											};
+											if (n.op != tkind.TK_ASSIGN) {
+												// Compound on direct struct-local
+												// scalar field: load current → push
+												// → eval rhs → combine → store
+												// (mirror cgen.c:3477 local arm).
+												let lop: str = fieldloadop(c, fi);
+												emitline("\t");
+												emitline(lop);
+												emitline("\t");
+												emitoff((lc.off + fi.foff): i64);
+												emitline("(BP), BX\n");
+												emitline("\tPUSHQ\tBX\n");
+											};
 											cgexpr(c, n.rhs);
+											if (n.op != tkind.TK_ASSIGN) {
+												emitline("\tPOPQ\tBX\n");
+												// PLUSEQ commutes; MINUSEQ needs
+												// lhs-rhs (BX old lhs, AX rhs).
+												if (n.op == tkind.TK_PLUSEQ)  { emitline("\tADDQ\tBX, AX\n"); };
+												if (n.op == tkind.TK_MINUSEQ) {
+													emitline("\tSUBQ\tAX, BX\n");
+													emitline("\tMOVQ\tBX, AX\n");
+												};
+											};
 											// str/slice field direct: str IS []u8, so both store the
 											// full 3-word {ptr,len,cap} from (AX,BX,CX) at +0/+8/+16.
 											// BP base, no scratch reload needed; the generic fldstoreop
@@ -5751,6 +5774,26 @@ fn cgassign(c: *cgen, n: *node) void = {
 										return;
 									};
 								};
+								if (n.op != tkind.TK_ASSIGN) {
+									// Compound on local `str|slice` pseudo-field:
+									// load current → push → eval rhs → combine →
+									// store (mirror cgen.c:3235 local arm).
+									emitline("\tMOVQ\t");
+									emitoff((lc.off + delta): i64);
+									emitline("(BP), BX\n");
+									emitline("\tPUSHQ\tBX\n");
+									cgexpr(c, n.rhs);
+									emitline("\tPOPQ\tBX\n");
+									if (n.op == tkind.TK_PLUSEQ)  { emitline("\tADDQ\tBX, AX\n"); };
+									if (n.op == tkind.TK_MINUSEQ) {
+										emitline("\tSUBQ\tAX, BX\n");
+										emitline("\tMOVQ\tBX, AX\n");
+									};
+									emitline("\tMOVQ\tAX, ");
+									emitoff((lc.off + delta): i64);
+									emitline("(BP)\n");
+									return;
+								};
 								cgexpr(c, n.rhs);
 								emitline("\tMOVQ\tAX, ");
 								emitoff((lc.off + delta): i64);
diff --git a/selfhost/cmd/wwdump/main.combined.ww b/selfhost/cmd/wwdump/main.combined.ww
index 51450350..21ff61ac 100644
--- a/selfhost/cmd/wwdump/main.combined.ww
+++ b/selfhost/cmd/wwdump/main.combined.ww
@@ -24299,7 +24299,30 @@ fn cgassign(c: *cgen, n: *node) void = {
 													return;
 												};};
 											};
+											if (n.op != tkind.TK_ASSIGN) {
+												// Compound on direct struct-local
+												// scalar field: load current → push
+												// → eval rhs → combine → store
+												// (mirror cgen.c:3477 local arm).
+												let lop: str = fieldloadop(c, fi);
+												emitline("\t");
+												emitline(lop);
+												emitline("\t");
+												emitoff((lc.off + fi.foff): i64);
+												emitline("(BP), BX\n");
+												emitline("\tPUSHQ\tBX\n");
+											};
 											cgexpr(c, n.rhs);
+											if (n.op != tkind.TK_ASSIGN) {
+												emitline("\tPOPQ\tBX\n");
+												// PLUSEQ commutes; MINUSEQ needs
+												// lhs-rhs (BX old lhs, AX rhs).
+												if (n.op == tkind.TK_PLUSEQ)  { emitline("\tADDQ\tBX, AX\n"); };
+												if (n.op == tkind.TK_MINUSEQ) {
+													emitline("\tSUBQ\tAX, BX\n");
+													emitline("\tMOVQ\tBX, AX\n");
+												};
+											};
 											// str/slice field direct: str IS []u8, so both store the
 											// full 3-word {ptr,len,cap} from (AX,BX,CX) at +0/+8/+16.
 											// BP base, no scratch reload needed; the generic fldstoreop
@@ -24392,6 +24415,26 @@ fn cgassign(c: *cgen, n: *node) void = {
 										return;
 									};
 								};
+								if (n.op != tkind.TK_ASSIGN) {
+									// Compound on local `str|slice` pseudo-field:
+									// load current → push → eval rhs → combine →
+									// store (mirror cgen.c:3235 local arm).
+									emitline("\tMOVQ\t");
+									emitoff((lc.off + delta): i64);
+									emitline("(BP), BX\n");
+									emitline("\tPUSHQ\tBX\n");
+									cgexpr(c, n.rhs);
+									emitline("\tPOPQ\tBX\n");
+									if (n.op == tkind.TK_PLUSEQ)  { emitline("\tADDQ\tBX, AX\n"); };
+									if (n.op == tkind.TK_MINUSEQ) {
+										emitline("\tSUBQ\tAX, BX\n");
+										emitline("\tMOVQ\tBX, AX\n");
+									};
+									emitline("\tMOVQ\tAX, ");
+									emitoff((lc.off + delta): i64);
+									emitline("(BP)\n");
+									return;
+								};
 								cgexpr(c, n.rhs);
 								emitline("\tMOVQ\tAX, ");
 								emitoff((lc.off + delta): i64);
diff --git a/test/wcc/data/attest_pass.ww b/test/wcc/data/attest_pass.ww
index ac70e6ce..40119e2a 100644
--- a/test/wcc/data/attest_pass.ww
+++ b/test/wcc/data/attest_pass.ww
@@ -2,6 +2,8 @@
 
 package data;
 
+type point = struct { x: i32, y: i32 };
+
 @test fn check_add() void = {
 	let a: i32 = 2;
 	let b: i32 = 3;
@@ -21,3 +23,24 @@ package data;
 		let _: i32 = 1 / 0;
 	};
 };
+
+// #227: compound assign (`-=`/`+=`) on a local field must
+// load-combine-store, not drop the op. Pre-fix wwstage stored the bare
+// rhs (p.x->4, p.y->5, view.len->1), so each mismatch aborts via 1/0.
+@test fn check_local_field_compound() void = {
+	let p: point = point { x = 10i32, y = 3i32 };
+	p.x -= 4i32;
+	p.y += 5i32;
+	if (p.x != 6) {
+		let _: i32 = 1 / 0;
+	};
+	if (p.y != 8) {
+		let _: i32 = 1 / 0;
+	};
+	let view: str = "hello";
+	view.len -= 1;
+	let n: i32 = view.len: i32;
+	if (n != 4) {
+		let _: i32 = 1 / 0;
+	};
+};