diff --git a/Makefile b/Makefile
index 1e4eac99..f38d3010 100644
--- a/Makefile
+++ b/Makefile
@@ -333,6 +333,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_f64xmm_run \
 	  $(BIN)/test_tuprecv_f64_run \
 	  $(BIN)/test_floats_run \
+	  $(BIN)/test_size_type_run \
 	  $(BIN)/test_bufio_run $(BIN)/test_random_run
 
 $(BIN)/test_smoke: test/wcc/000_smoke.c $(LIB)/libwcc.a | $(BIN)
@@ -1074,6 +1075,10 @@ $(BIN)/test_floats_run: test/wcc/952_floats_run.c $(BIN)/ww $(BIN)/w6c \
 		$(BIN)/w6a $(BIN)/w6l $(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_size_type_run: test/wcc/957_size_type_run.c $(BIN)/ww $(BIN)/w6c \
+		$(BIN)/w6a $(BIN)/w6l $(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 $(BIN)/test_f64crossmod_run: test/wcc/953_f64crossmod_run.c $(BIN)/ww \
 		$(BIN)/w6c $(BIN)/w6c_ww $(BIN)/w6a $(BIN)/w6l \
 		$(LIB)/libwwrt.a | $(BIN)
diff --git a/cmd/wcc/check.c b/cmd/wcc/check.c
index 19c4d34e..40ebef79 100644
--- a/cmd/wcc/check.c
+++ b/cmd/wcc/check.c
@@ -49,6 +49,7 @@ lookup_builtin(const char *name)
 	if (strcmp(name, "int") == 0)     return ty_int;
 	if (strcmp(name, "uint") == 0)    return ty_uint;
 	if (strcmp(name, "uintptr") == 0) return ty_uintptr;
+	if (strcmp(name, "size") == 0)    return ty_size;	/* #85 fold-2 */
 	if (strcmp(name, "f32") == 0)     return ty_f32;
 	if (strcmp(name, "f64") == 0)     return ty_f64;
 	if (strcmp(name, "str") == 0)     return ty_str;
diff --git a/selfhost/cmd/w6c/main.combined.ww b/selfhost/cmd/w6c/main.combined.ww
index e4a3c687..5a812483 100644
--- a/selfhost/cmd/w6c/main.combined.ww
+++ b/selfhost/cmd/w6c/main.combined.ww
@@ -7836,7 +7836,7 @@ fn primtypesize(nm: str) i64 = {
 	if (streq(nm, "i16") || streq(nm, "u16")) { return 2i64; };
 	if (streq(nm, "i32") || streq(nm, "u32") || streq(nm, "f32") || streq(nm, "rune")) { return 4i64; };
 	if (streq(nm, "i64") || streq(nm, "u64") || streq(nm, "f64")) { return 8i64; };
-	if (streq(nm, "int") || streq(nm, "uint") || streq(nm, "uintptr")) { return 8i64; };
+	if (streq(nm, "int") || streq(nm, "uint") || streq(nm, "uintptr") || streq(nm, "size")) { return 8i64; };
 	// str IS []u8: 24B, sourced from the slice header SSoT so str and
 	// []u8 can never drift; no second hardcoded 24 (#1/Phase 3).
 	if (streq(nm, "str")) { return tyslicesize(); };
@@ -7895,7 +7895,7 @@ fn astalign(c: *checker, t: *node) i64 = {
 		if (streq(nm, "void") || streq(nm, "bool") || streq(nm, "i8") || streq(nm, "u8")) { return 1i64; };
 		if (streq(nm, "i16") || streq(nm, "u16")) { return 2i64; };
 		if (streq(nm, "i32") || streq(nm, "u32") || streq(nm, "f32") || streq(nm, "rune")) { return 4i64; };
-		if (streq(nm, "i64") || streq(nm, "u64") || streq(nm, "f64") || streq(nm, "int") || streq(nm, "uint") || streq(nm, "uintptr") || streq(nm, "str")) { return 8i64; };
+		if (streq(nm, "i64") || streq(nm, "u64") || streq(nm, "f64") || streq(nm, "int") || streq(nm, "uint") || streq(nm, "uintptr") || streq(nm, "size") || streq(nm, "str")) { return 8i64; };
 		let resolved: *node = resolvealias(c, t);
 		if (resolved != nil && resolved != t) {
 			return astalign(c, resolved);
@@ -8421,6 +8421,7 @@ fn tinfofornode(c: *checker, n: *node) *tinfo = {
 		if (streq(nm, "int"))            { r = c.tc.tyint; };
 		if (streq(nm, "uint"))           { r = c.tc.tyuint; };
 		if (streq(nm, "uintptr"))        { r = c.tc.tyuintptr; };
+		if (streq(nm, "size"))           { r = c.tc.tysize; };	// #85 fold-2
 		if (streq(nm, "f32"))            { r = c.tc.tyf32; };
 		if (streq(nm, "f64"))            { r = c.tc.tyf64; };
 		if (streq(nm, "str"))            { r = c.tc.tystr; };
@@ -9713,6 +9714,7 @@ fn isinttypeast(t: *node) bool = {
 	if (streq(s, "int"))  { return true; };
 	if (streq(s, "uint")) { return true; };
 	if (streq(s, "uintptr")) { return true; };
+	if (streq(s, "size")) { return true; };
 	if (streq(s, "rune")) { return true; };
 	return false;
 };
@@ -9732,6 +9734,7 @@ fn isnumerictname(t: *node) bool = {
 	if (streq(s, "int"))  { return true; };
 	if (streq(s, "uint")) { return true; };
 	if (streq(s, "uintptr")) { return true; };
+	if (streq(s, "size")) { return true; };
 	if (streq(s, "rune")) { return true; };
 	if (streq(s, "f32"))  { return true; };
 	if (streq(s, "f64"))  { return true; };
@@ -11986,6 +11989,7 @@ fn primsize(name: str) i32 = {
 	if (streq(name, "uint")) { return 8; };
 	if (streq(name, "int"))  { return 8; };
 	if (streq(name, "uintptr")) { return 8; };
+	if (streq(name, "size")) { return 8; };
 	if (streq(name, "f64"))  { return 8; };
 	if (streq(name, "rune")) { return 4; };
 	if (streq(name, "void")) { return 0; };
@@ -23454,6 +23458,7 @@ fn letscalarprim(nm: str) bool = {
 	if (streq(nm, "int"))  { return true; };
 	if (streq(nm, "uint")) { return true; };
 	if (streq(nm, "uintptr")) { return true; };
+	if (streq(nm, "size")) { return true; };
 	return false;
 };
 
diff --git a/selfhost/cmd/wcc/cgen.ww b/selfhost/cmd/wcc/cgen.ww
index d275445a..a4a57a46 100644
--- a/selfhost/cmd/wcc/cgen.ww
+++ b/selfhost/cmd/wcc/cgen.ww
@@ -904,6 +904,7 @@ fn letscalarprim(nm: str) bool = {
 	if (streq(nm, "int"))  { return true; };
 	if (streq(nm, "uint")) { return true; };
 	if (streq(nm, "uintptr")) { return true; };
+	if (streq(nm, "size")) { return true; };
 	return false;
 };
 
diff --git a/selfhost/cmd/wcc/cgenutil.ww b/selfhost/cmd/wcc/cgenutil.ww
index c5f51d21..404302c0 100644
--- a/selfhost/cmd/wcc/cgenutil.ww
+++ b/selfhost/cmd/wcc/cgenutil.ww
@@ -1248,6 +1248,7 @@ fn primsize(name: str) i32 = {
 	if (streq(name, "uint")) { return 8; };
 	if (streq(name, "int"))  { return 8; };
 	if (streq(name, "uintptr")) { return 8; };
+	if (streq(name, "size")) { return 8; };
 	if (streq(name, "f64"))  { return 8; };
 	if (streq(name, "rune")) { return 4; };
 	if (streq(name, "void")) { return 0; };
diff --git a/selfhost/cmd/wcc/check.ww b/selfhost/cmd/wcc/check.ww
index aa6e3e28..24109230 100644
--- a/selfhost/cmd/wcc/check.ww
+++ b/selfhost/cmd/wcc/check.ww
@@ -713,7 +713,7 @@ fn primtypesize(nm: str) i64 = {
 	if (streq(nm, "i16") || streq(nm, "u16")) { return 2i64; };
 	if (streq(nm, "i32") || streq(nm, "u32") || streq(nm, "f32") || streq(nm, "rune")) { return 4i64; };
 	if (streq(nm, "i64") || streq(nm, "u64") || streq(nm, "f64")) { return 8i64; };
-	if (streq(nm, "int") || streq(nm, "uint") || streq(nm, "uintptr")) { return 8i64; };
+	if (streq(nm, "int") || streq(nm, "uint") || streq(nm, "uintptr") || streq(nm, "size")) { return 8i64; };
 	// str IS []u8: 24B, sourced from the slice header SSoT so str and
 	// []u8 can never drift; no second hardcoded 24 (#1/Phase 3).
 	if (streq(nm, "str")) { return tyslicesize(); };
@@ -772,7 +772,7 @@ fn astalign(c: *checker, t: *node) i64 = {
 		if (streq(nm, "void") || streq(nm, "bool") || streq(nm, "i8") || streq(nm, "u8")) { return 1i64; };
 		if (streq(nm, "i16") || streq(nm, "u16")) { return 2i64; };
 		if (streq(nm, "i32") || streq(nm, "u32") || streq(nm, "f32") || streq(nm, "rune")) { return 4i64; };
-		if (streq(nm, "i64") || streq(nm, "u64") || streq(nm, "f64") || streq(nm, "int") || streq(nm, "uint") || streq(nm, "uintptr") || streq(nm, "str")) { return 8i64; };
+		if (streq(nm, "i64") || streq(nm, "u64") || streq(nm, "f64") || streq(nm, "int") || streq(nm, "uint") || streq(nm, "uintptr") || streq(nm, "size") || streq(nm, "str")) { return 8i64; };
 		let resolved: *node = resolvealias(c, t);
 		if (resolved != nil && resolved != t) {
 			return astalign(c, resolved);
@@ -1298,6 +1298,7 @@ fn tinfofornode(c: *checker, n: *node) *tinfo = {
 		if (streq(nm, "int"))            { r = c.tc.tyint; };
 		if (streq(nm, "uint"))           { r = c.tc.tyuint; };
 		if (streq(nm, "uintptr"))        { r = c.tc.tyuintptr; };
+		if (streq(nm, "size"))           { r = c.tc.tysize; };	// #85 fold-2
 		if (streq(nm, "f32"))            { r = c.tc.tyf32; };
 		if (streq(nm, "f64"))            { r = c.tc.tyf64; };
 		if (streq(nm, "str"))            { r = c.tc.tystr; };
@@ -2590,6 +2591,7 @@ fn isinttypeast(t: *node) bool = {
 	if (streq(s, "int"))  { return true; };
 	if (streq(s, "uint")) { return true; };
 	if (streq(s, "uintptr")) { return true; };
+	if (streq(s, "size")) { return true; };
 	if (streq(s, "rune")) { return true; };
 	return false;
 };
@@ -2609,6 +2611,7 @@ fn isnumerictname(t: *node) bool = {
 	if (streq(s, "int"))  { return true; };
 	if (streq(s, "uint")) { return true; };
 	if (streq(s, "uintptr")) { return true; };
+	if (streq(s, "size")) { return true; };
 	if (streq(s, "rune")) { return true; };
 	if (streq(s, "f32"))  { return true; };
 	if (streq(s, "f64"))  { return true; };
diff --git a/selfhost/cmd/wwdump/main.combined.ww b/selfhost/cmd/wwdump/main.combined.ww
index 75f2ac1e..68ab61df 100644
--- a/selfhost/cmd/wwdump/main.combined.ww
+++ b/selfhost/cmd/wwdump/main.combined.ww
@@ -7836,7 +7836,7 @@ fn primtypesize(nm: str) i64 = {
 	if (streq(nm, "i16") || streq(nm, "u16")) { return 2i64; };
 	if (streq(nm, "i32") || streq(nm, "u32") || streq(nm, "f32") || streq(nm, "rune")) { return 4i64; };
 	if (streq(nm, "i64") || streq(nm, "u64") || streq(nm, "f64")) { return 8i64; };
-	if (streq(nm, "int") || streq(nm, "uint") || streq(nm, "uintptr")) { return 8i64; };
+	if (streq(nm, "int") || streq(nm, "uint") || streq(nm, "uintptr") || streq(nm, "size")) { return 8i64; };
 	// str IS []u8: 24B, sourced from the slice header SSoT so str and
 	// []u8 can never drift; no second hardcoded 24 (#1/Phase 3).
 	if (streq(nm, "str")) { return tyslicesize(); };
@@ -7895,7 +7895,7 @@ fn astalign(c: *checker, t: *node) i64 = {
 		if (streq(nm, "void") || streq(nm, "bool") || streq(nm, "i8") || streq(nm, "u8")) { return 1i64; };
 		if (streq(nm, "i16") || streq(nm, "u16")) { return 2i64; };
 		if (streq(nm, "i32") || streq(nm, "u32") || streq(nm, "f32") || streq(nm, "rune")) { return 4i64; };
-		if (streq(nm, "i64") || streq(nm, "u64") || streq(nm, "f64") || streq(nm, "int") || streq(nm, "uint") || streq(nm, "uintptr") || streq(nm, "str")) { return 8i64; };
+		if (streq(nm, "i64") || streq(nm, "u64") || streq(nm, "f64") || streq(nm, "int") || streq(nm, "uint") || streq(nm, "uintptr") || streq(nm, "size") || streq(nm, "str")) { return 8i64; };
 		let resolved: *node = resolvealias(c, t);
 		if (resolved != nil && resolved != t) {
 			return astalign(c, resolved);
@@ -8421,6 +8421,7 @@ fn tinfofornode(c: *checker, n: *node) *tinfo = {
 		if (streq(nm, "int"))            { r = c.tc.tyint; };
 		if (streq(nm, "uint"))           { r = c.tc.tyuint; };
 		if (streq(nm, "uintptr"))        { r = c.tc.tyuintptr; };
+		if (streq(nm, "size"))           { r = c.tc.tysize; };	// #85 fold-2
 		if (streq(nm, "f32"))            { r = c.tc.tyf32; };
 		if (streq(nm, "f64"))            { r = c.tc.tyf64; };
 		if (streq(nm, "str"))            { r = c.tc.tystr; };
@@ -9713,6 +9714,7 @@ fn isinttypeast(t: *node) bool = {
 	if (streq(s, "int"))  { return true; };
 	if (streq(s, "uint")) { return true; };
 	if (streq(s, "uintptr")) { return true; };
+	if (streq(s, "size")) { return true; };
 	if (streq(s, "rune")) { return true; };
 	return false;
 };
@@ -9732,6 +9734,7 @@ fn isnumerictname(t: *node) bool = {
 	if (streq(s, "int"))  { return true; };
 	if (streq(s, "uint")) { return true; };
 	if (streq(s, "uintptr")) { return true; };
+	if (streq(s, "size")) { return true; };
 	if (streq(s, "rune")) { return true; };
 	if (streq(s, "f32"))  { return true; };
 	if (streq(s, "f64"))  { return true; };
@@ -11986,6 +11989,7 @@ fn primsize(name: str) i32 = {
 	if (streq(name, "uint")) { return 8; };
 	if (streq(name, "int"))  { return 8; };
 	if (streq(name, "uintptr")) { return 8; };
+	if (streq(name, "size")) { return 8; };
 	if (streq(name, "f64"))  { return 8; };
 	if (streq(name, "rune")) { return 4; };
 	if (streq(name, "void")) { return 0; };
@@ -23454,6 +23458,7 @@ fn letscalarprim(nm: str) bool = {
 	if (streq(nm, "int"))  { return true; };
 	if (streq(nm, "uint")) { return true; };
 	if (streq(nm, "uintptr")) { return true; };
+	if (streq(nm, "size")) { return true; };
 	return false;
 };
 
diff --git a/test/wcc/957_size_type_run.c b/test/wcc/957_size_type_run.c
new file mode 100644
index 00000000..05d643e6
--- /dev/null
+++ b/test/wcc/957_size_type_run.c
@@ -0,0 +1,137 @@
+/*
+ * 957_size_type_run — runtime proof that the `size` type name is usable
+ * in TYPE position (#85 fold-2) and that it coexists with the `size(T)`
+ * size-of OPERATOR. The two are different paths — TYPE-position `size`
+ * resolves via the type-name resolver (lookup_builtin / tinfofornode's
+ * N_TNAME chain), while `size(T)` is a c.top SK_FN seed folded to an
+ * N_INTLIT — so a program may use BOTH in the same scope with no clash.
+ * Each row below exercises that coexistence; without the fold-2 resolver
+ * arm the `let _: size` rows fail to compile ("unknown type 'size'"), so
+ * a green row IS the proof the name binds.
+ *
+ * `size` mirrors uintptr: platform-width (8B amd64) unsigned int. The
+ * rows assert it is usable in arithmetic, comparison, and an i32 cast.
+ *
+ * Table-driven like 952_floats_run: each row is a self-contained ww
+ * program; the C-side cstage `ww build -I lib` compiles it, we run the
+ * binary and assert the exit code. cstage-only by design (mirrors 951/
+ * 952/969): `ww_ww run` is broken (#95) and per-program wwstage byte-id
+ * is the 990-997 gates' job; the wwstage resolver arm is twinned for
+ * rule-10 symmetry and stays dead on the size-free selfhost corpus.
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+
+static int
+runwait(const char *cmd)
+{
+	int rc = system(cmd);
+	if (rc == -1) return -1;
+	if (WIFEXITED(rc)) return WEXITSTATUS(rc);
+	return 1;
+}
+
+struct row { const char *src; int want_exit; };
+
+static const struct row rows[] = {
+	/* type-position `size` + the size(T) operator in one scope. x is a
+	 * size-typed local; size(int)/size(i32) are folded operator results.
+	 * Both must resolve and agree (8/4 on amd64). */
+	{ "package main;\n"
+	  "export fn main() i32 = {\n"
+	  "	let x: size = 0;\n"
+	  "	if (x != 0) { return 1; };\n"
+	  "	let y: size = 42;\n"
+	  "	if (y != 42) { return 2; };\n"
+	  "	if (size(int) != 8) { return 3; };\n"
+	  "	if (size(i32) != 4) { return 4; };\n"
+	  "	return 0;\n"
+	  "};\n", 0 },
+	/* size arithmetic + i32 cast value propagation: a size-typed sum
+	 * truncates to i32 and propagates (40 + 2 == 42). */
+	{ "package main;\n"
+	  "export fn main() i32 = {\n"
+	  "	let x: size = 40;\n"
+	  "	let y: size = 2;\n"
+	  "	return (x + y): i32;\n"
+	  "};\n", 42 },
+	/* size as a struct field type: 8-byte slot, written and read back. */
+	{ "package main;\n"
+	  "type box = struct { n: size };\n"
+	  "export fn main() i32 = {\n"
+	  "	let b: box = box{ n = 7 };\n"
+	  "	return b.n: i32;\n"
+	  "};\n", 7 },
+	/* the size(T) operator value-propagated through an i32 cast (operator
+	 * path, must keep working alongside the new type-name arm). */
+	{ "package main;\n"
+	  "export fn main() i32 = {\n"
+	  "	return size(int): i32;\n"
+	  "};\n", 8 },
+	{ NULL, 0 }
+};
+
+int
+main(void)
+{
+	const char *bin = getenv("BIN");
+	if (!bin) bin = "out/bin";
+	char cwd[1024];
+	if (getcwd(cwd, sizeof cwd) == NULL) return 1;
+	char absbin[1024];
+	if (bin[0] != '/') {
+		snprintf(absbin, sizeof absbin, "%s/%s", cwd, bin);
+		bin = absbin;
+	}
+
+	int n = 0, fail = 0;
+	for (int i = 0; rows[i].src; i++, n++) {
+		char src[64];
+		snprintf(src, sizeof src, "/tmp/wwsz_%d_%d.ww", getpid(), i);
+
+		FILE *f = fopen(src, "wb");
+		if (f == NULL) { fail++; continue; }
+		fputs(rows[i].src, f);
+		fclose(f);
+
+		char tmpdir[64];
+		snprintf(tmpdir, sizeof tmpdir, "/tmp/wwsz_%d_d_%d", getpid(), i);
+		mkdir(tmpdir, 0755);
+
+		char cmd[2048];
+		snprintf(cmd, sizeof cmd, "cd %s && %s/ww build -I %s/lib %s",
+		    tmpdir, bin, cwd, src);
+		if (runwait(cmd) != 0) {
+			fprintf(stderr, "row %d: build failed\n  src: %s\n",
+			    i, rows[i].src);
+			fail++;
+			unlink(src); rmdir(tmpdir);
+			continue;
+		}
+
+		char outbin[128];
+		const char *base = strrchr(src, '/');
+		base = base ? base + 1 : src;
+		snprintf(outbin, sizeof outbin, "%s/%s", tmpdir, base);
+		char *dot = strrchr(outbin, '.');
+		if (dot && strcmp(dot, ".ww") == 0) *dot = '\0';
+
+		int got = runwait(outbin);
+		if (got != rows[i].want_exit) {
+			fprintf(stderr, "row %d: exit %d, want %d\n  src: %s\n",
+			    i, got, rows[i].want_exit, rows[i].src);
+			fail++;
+		}
+		unlink(src); unlink(outbin); rmdir(tmpdir);
+	}
+	if (fail) {
+		fprintf(stderr, "%d/%d size_type tests failed\n", fail, n);
+		return 1;
+	}
+	printf("size_type: %d/%d ok\n", n, n);
+	return 0;
+}