diff --git a/include/jets/k.h b/include/jets/k.h
index 3edde2142..0d06a9a64 100644
--- a/include/jets/k.h
+++ b/include/jets/k.h
@@ -43,6 +43,11 @@
     u3_noun
     u3kc_rip(u3_atom a, u3_atom b);
 
+  /* u3kc_swp(): reverse block order.
+  */
+    u3_noun
+    u3kc_swp(u3_atom a, u3_atom b);
+
 /* u3kd: tier 4 functions
 */
   /* u3kdb_get(): map get for key `b` in map `a` with u3_none.
diff --git a/include/jets/q.h b/include/jets/q.h
index 48db0ea5e..6a7763a85 100644
--- a/include/jets/q.h
+++ b/include/jets/q.h
@@ -66,6 +66,7 @@
     u3_noun u3qc_rep(u3_atom, u3_noun);
     u3_noun u3qc_rip(u3_atom, u3_atom);
     u3_noun u3qc_rsh(u3_atom, u3_atom, u3_atom);
+    u3_noun u3qc_swp(u3_atom, u3_atom);
     u3_noun u3qc_sqt(u3_atom);
     u3_noun u3qc_vor(u3_atom, u3_atom);
 
diff --git a/include/jets/w.h b/include/jets/w.h
index 693cff4ba..0993ab563 100644
--- a/include/jets/w.h
+++ b/include/jets/w.h
@@ -66,6 +66,7 @@
     u3_noun u3wc_rep(u3_noun);
     u3_noun u3wc_rip(u3_noun);
     u3_noun u3wc_rsh(u3_noun);
+    u3_noun u3wc_swp(u3_noun);
     u3_noun u3wc_sqt(u3_noun);
     u3_noun u3wc_vor(u3_noun);
 
diff --git a/jets/c/swp.c b/jets/c/swp.c
new file mode 100644
index 000000000..1b10dca2b
--- /dev/null
+++ b/jets/c/swp.c
@@ -0,0 +1,39 @@
+/* j/3/swp.c
+**
+*/
+#include "all.h"
+
+/* functions
+*/
+
+  u3_noun
+  u3qc_swp(u3_atom a,
+           u3_atom b)
+  {
+    //XX write a proper c-style swp, maybe
+    return u3kc_rep(u3k(a), u3kb_flop(u3qc_rip(a, b)));
+  }
+
+  u3_noun
+  u3wc_swp(u3_noun cor)
+  {
+    u3_noun a, b;
+
+    if ( (c3n == u3r_mean(cor, u3x_sam_2, &a, u3x_sam_3, &b, 0)) ||
+         (c3n == u3ud(a)) ||
+         (c3n == u3ud(b)) )
+    {
+      return u3m_bail(c3__exit);
+    } else {
+      return u3qc_swp(a, b);
+    }
+  }
+
+  u3_noun
+  u3kc_swp(u3_atom a,
+           u3_atom b)
+  {
+    u3_noun res = u3qc_swp(a, b);
+    u3z(a); u3z(b);
+    return res;
+  }
diff --git a/jets/tree.c b/jets/tree.c
index 784ae0607..e82317c87 100644
--- a/jets/tree.c
+++ b/jets/tree.c
@@ -512,6 +512,7 @@ static u3j_core _143_tri_d[] =
   static u3j_harm _143_two_rep_a[] = {{".2", u3wc_rep, c3y}, {}};
   static u3j_harm _143_two_rip_a[] = {{".2", u3wc_rip, c3y}, {}};
   static u3j_harm _143_two_rsh_a[] = {{".2", u3wc_rsh, c3y}, {}};
+  static u3j_harm _143_two_swp_a[] = {{".2", u3wc_swp, c3y}, {}};
   static u3j_harm _143_two_sqt_a[] = {{".2", u3wc_sqt, c3y}, {}};
   static u3j_harm _143_two_vor_a[] = {{".2", u3wc_vor, c3y}, {}};
   static u3j_harm _143_two_xeb_a[] = {{".2", u3wc_xeb, c3y}, {}};
@@ -618,12 +619,14 @@ static u3j_core _143_two_d[] =
     { "rub", _143_two_rub_a },
     { "peg", _143_two_peg_a },
     { "pow", _143_two_pow_a },
+    { "swp", _143_two_swp_a },
     { "sqt", _143_two_sqt_a },
     { "vor", _143_two_vor_a },
     { "xeb", _143_two_xeb_a },
 
     { "by", 0, _143_two__by_d },
     { "in", 0, _143_two__in_d },
+    {}
   };
 
 
diff --git a/meson.build b/meson.build
index e89ab0793..772c84c63 100644
--- a/meson.build
+++ b/meson.build
@@ -73,6 +73,7 @@ jets_c_src = [
 'jets/c/rep.c',
 'jets/c/rip.c',
 'jets/c/rsh.c',
+'jets/c/swp.c',
 'jets/c/sqt.c',
 'jets/c/vor.c',
 ]