diff --git a/examples/0043-basic-match-value-mixed-width.sx b/examples/0043-basic-match-value-mixed-width.sx
new file mode 100644
index 0000000..fb46ce4
--- /dev/null
+++ b/examples/0043-basic-match-value-mixed-width.sx
@@ -0,0 +1,31 @@
+// A value-position match (`if subject == { case … }`) returning a small
+// integer type works when arms mix positive and negated literals: every arm
+// value is lowered against the merge's result type, so the phi operands all
+// share one width.
+//
+// Regression (issue 0066): a negated-literal arm (`else: -1`) previously
+// lowered at a narrower width than the positive arms, tripping LLVM's
+// "PHI node operands are not the same type as the result".
+
+#import "modules/std.sx";
+
+sign :: (n: s32) -> s32 {
+    if n == {
+        case 0:  0;
+        else:    if n > 0 then 1 else -1;
+    }
+}
+
+classify :: (n: s32) -> s32 {
+    if n == {
+        case 0:  100;
+        case 1:  10;
+        else:    -1;
+    }
+}
+
+main :: () -> s32 {
+    print("sign: {} {} {}\n", sign(-9), sign(0), sign(9));   // -1 0 1
+    print("classify: {} {} {}\n", classify(0), classify(1), classify(5)); // 100 10 -1
+    0
+}
diff --git a/examples/expected/0043-basic-match-value-mixed-width.exit b/examples/expected/0043-basic-match-value-mixed-width.exit
new file mode 100644
index 0000000..573541a
--- /dev/null
+++ b/examples/expected/0043-basic-match-value-mixed-width.exit
@@ -0,0 +1 @@
+0
diff --git a/examples/expected/0043-basic-match-value-mixed-width.stderr b/examples/expected/0043-basic-match-value-mixed-width.stderr
new file mode 100644
index 0000000..8b13789
--- /dev/null
+++ b/examples/expected/0043-basic-match-value-mixed-width.stderr
@@ -0,0 +1 @@
+
diff --git a/examples/expected/0043-basic-match-value-mixed-width.stdout b/examples/expected/0043-basic-match-value-mixed-width.stdout
new file mode 100644
index 0000000..24232c6
--- /dev/null
+++ b/examples/expected/0043-basic-match-value-mixed-width.stdout
@@ -0,0 +1,2 @@
+sign: -1 0 1
+classify: 100 10 -1
diff --git a/issues/0066-match-arm-negative-literal-phi-width.md b/issues/0066-match-arm-negative-literal-phi-width.md
index c906641..f40b7a5 100644
--- a/issues/0066-match-arm-negative-literal-phi-width.md
+++ b/issues/0066-match-arm-negative-literal-phi-width.md
@@ -1,5 +1,11 @@
 # 0066 — match-as-value with a negated-literal arm builds a mismatched phi
 
+> **RESOLVED.** `lowerMatch`'s value path (`has_value_merge`) now lowers each
+> arm body with `target_type = result_type`, so literals and negated literals in
+> the arms pick the merge's width instead of leaking a narrower one. The phi
+> operands are uniform; `coerceToType` still runs afterward as a backstop.
+> Regression: `examples/0043-basic-match-value-mixed-width.sx`.
+
 ## Symptom
 
 A value-position `match` (the `if subject == { case ... }` sugar) returning a
diff --git a/src/ir/lower.zig b/src/ir/lower.zig
index 35ba192..f96a202 100644
--- a/src/ir/lower.zig
+++ b/src/ir/lower.zig
@@ -4497,7 +4497,13 @@ pub const Lowering = struct {
             }
 
             if (has_value_merge) {
+                // Lower the arm body against the merge's result type so literals
+                // (and negated literals) in the arm pick the right width — the
+                // phi operands must all match `result_type` (issue 0066).
+                const saved_arm_target = self.target_type;
+                self.target_type = result_type;
                 const maybe_v = self.lowerBlockValue(arm.body);
+                self.target_type = saved_arm_target;
                 self.current_match_tags = saved_match_tags;
                 self.scope = old_scope;
                 arm_scope.deinit();