diff --git a/libs/gamecode/Makemodule.am b/libs/gamecode/Makemodule.am
index b3d26d62f..748fdb635 100644
--- a/libs/gamecode/Makemodule.am
+++ b/libs/gamecode/Makemodule.am
@@ -21,7 +21,12 @@ libs_gamecode_libQFgamecode_la_SOURCES= \
 	libs/gamecode/pr_v6p_opcode.c \
 	libs/gamecode/pr_zone.c
 
-noinst_PYTHON += $(opcodes_py) $(convert_py) $(hops_py) $(swizzle_py)
+noinst_PYTHON += \
+	$(opcodes_py) \
+	$(convert_py) \
+	${extend_py} \
+	$(hops_py) \
+	$(swizzle_py)
 
 opcodes_py = $(srcdir)/libs/gamecode/opcodes.py
 pr_opcode_cinc = $(top_builddir)/libs/gamecode/pr_opcode.cinc
@@ -34,6 +39,9 @@ libs/gamecode/pr_opcode.lo: libs/gamecode/pr_opcode.c ${pr_opcode_src}
 convert_py = $(srcdir)/libs/gamecode/convert.py
 pr_convert_cinc = $(top_builddir)/libs/gamecode/pr_convert.cinc
 
+extend_py = $(srcdir)/libs/gamecode/extend.py
+pr_extend_cinc = $(top_builddir)/libs/gamecode/pr_extend.cinc
+
 hops_py = $(srcdir)/libs/gamecode/hops.py
 pr_hops_cinc = $(top_builddir)/libs/gamecode/pr_hops.cinc
 
@@ -45,6 +53,7 @@ BUILT_SOURCES += \
 	$(pr_opcode_cinc) \
 	$(pr_opcode_hinc) \
 	$(pr_convert_cinc) \
+	$(pr_extend_cinc) \
 	$(pr_hops_cinc) \
 	$(pr_swizzle32_cinc) \
 	$(pr_swizzle64_cinc)
@@ -53,6 +62,7 @@ CLEANFILES += \
 	$(pr_opcode_cinc) \
 	$(pr_opcode_hinc) \
 	$(pr_convert_cinc) \
+	$(pr_extend_cinc) \
 	$(pr_hops_cinc) \
 	$(pr_swizzle32_cinc) \
 	$(pr_swizzle64_cinc)
@@ -70,6 +80,10 @@ $(pr_convert_cinc): $(convert_py)
 	$(V_PY)$(PYTHON) $(convert_py) table > $(pr_convert_cinc).t && \
 	$(am__mv) $(pr_convert_cinc).t $(pr_convert_cinc)
 
+$(pr_extend_cinc): $(extend_py)
+	$(V_PY)$(PYTHON) $(extend_py) table > $(pr_extend_cinc).t && \
+	$(am__mv) $(pr_extend_cinc).t $(pr_extend_cinc)
+
 $(pr_hops_cinc): $(hops_py)
 	$(V_PY)$(PYTHON) $(hops_py) table > $(pr_hops_cinc).t && \
 	$(am__mv) $(pr_hops_cinc).t $(pr_hops_cinc)
diff --git a/libs/gamecode/extend.py b/libs/gamecode/extend.py
new file mode 100644
index 000000000..99aa9ed81
--- /dev/null
+++ b/libs/gamecode/extend.py
@@ -0,0 +1,77 @@
+print("""// encoding is teemmm
+// t = 0: 32-bit, t = 1: 64-bit
+// e = 00: 0
+// e = 01: 1.0
+// e = 10: copy (1-n, 2-4, otherwise 0)
+// e = 11: -1.0
+// mmm = 000: 1 -> 2
+// mmm = 001: 1 -> 3
+// mmm = 010: 1 -> 4
+// mmm = 011: 2 -> 3
+// mmm = 100: 2 -> 4
+// mmm = 101: 3 -> 4
+// mmm = 110: reserved
+// mmm = 111: reserved
+""")
+
+types = [
+    ["ivec2", "ivec3", "ivec4", "ivec3", "ivec4", "ivec4"],
+    ["lvec2", "lvec3", "lvec4", "lvec3", "lvec4", "lvec4"],
+]
+
+src_types = [
+    ["int", "int", "int", "ivec2", "ivec2", "ivec3"],
+    ["long", "long", "long", "lvec2", "lvec2", "lvec3"],
+]
+
+extend = [
+    ["0", "INT32_C(0x3f800000)", "0", "INT32_C(0xbf800000)"],
+    ["0", "INT64_C(0x3ff0000000000000)", "0", "INT64_C(0xbff0000000000000)"],
+]
+
+def case_str(type, ext, mode):
+    case = (type << 5) | (ext << 3) | (mode)
+    return f"case {case:03o}:"
+
+def dst_str(type, ext, mode):
+    return f"OPC({types[type][mode]})"
+
+def cast_str(type, ext, mode):
+    return f"(pr_{types[type][mode]}_t)"
+
+def init_str(type, ext, mode):
+    ext_str = extend[type][ext]
+    src = f"OPA({src_types[type][mode]})"
+    if mode == 0:
+        if ext == 2:
+            ext_str = src
+        return f"{src}, {ext_str}"
+    elif mode == 1:
+        if ext == 2:
+            ext_str = src
+        return f"{src}, {ext_str}, {ext_str}"
+    elif mode == 2:
+        if ext == 2:
+            ext_str = src
+        return f"{src}, {ext_str}, {ext_str}, {ext_str}"
+    elif mode == 3:
+        return f"{src}[0], {src}[1], {ext_str}"
+    elif mode == 4:
+        if ext == 2:
+            return f"{src}[0], {src}[1], {src}[0], {src}[1]"
+        else:
+            return f"{src}[0], {src}[1], {ext_str}, {ext_str}"
+    elif mode == 5:
+        return f"{src}[0], {src}[1], {src}[2], {ext_str}"
+
+for type in range(2):
+    for ext in range(4):
+        for mode in range(6): # 6, 7 are reserved
+            case = case_str(type, ext, mode)
+            dst = dst_str(type, ext, mode)
+            cast = cast_str(type, ext, mode)
+            init = init_str(type, ext, mode)
+            if mode in [1, 3]:
+                print(f"{case} VectorSet({init}, {dst}); break;");
+            else:
+                print(f"{case} {dst} = {cast} {{ {init} }}; break;");
diff --git a/libs/gamecode/opcodes.py b/libs/gamecode/opcodes.py
index 4ec39a71f..79e1949d9 100644
--- a/libs/gamecode/opcodes.py
+++ b/libs/gamecode/opcodes.py
@@ -34,7 +34,7 @@ bitmap_txt = """
 1 1111 10oo fbitops
 1 1111 1100 convert (conversion mode in st->b)
 1 1111 1101 with (mode in st->a, value in st->b, reg in st->c)
-1 1111 1110
+1 1111 1110 extend
 1 1111 1111 hops
 """
 
@@ -204,6 +204,14 @@ fbitops_formats = {
         ],
     },
 }
+extend_formats = {
+    "opcode": "OP_EXTEND",
+    "mnemonic": "extend",
+    "opname": "extend",
+    "format": "%Ga %Hb %gc",
+    "widths": "-1, 0, -1",
+    "types": "ev_void, ev_short, ev_void",
+}
 hops_formats = {
     "opcode": "OP_HOPS",
     "mnemonic": "hops",
@@ -566,6 +574,7 @@ group_map = {
     "compare2": compare2_formats,
     "constant": constant_formats,
     "convert":  convert_formats,
+    "extend":   extend_formats,
     "fbitops":  fbitops_formats,
     "hops":     hops_formats,
     "jump":     jump_formats,
diff --git a/libs/gamecode/pr_exec.c b/libs/gamecode/pr_exec.c
index e8c4f2551..cab230ad6 100644
--- a/libs/gamecode/pr_exec.c
+++ b/libs/gamecode/pr_exec.c
@@ -2835,7 +2835,13 @@ pr_exec_ruamoko (progs_t *pr, int exitdepth)
 			case OP_WITH:
 				pr_with (pr, st);
 				break;
-			//        1110 spare
+			case OP_EXTEND:
+				switch (st->b) {
+#include "libs/gamecode/pr_extend.cinc"
+					default:
+						PR_RunError (pr, "invalid extend code: %04o", st->b);
+				}
+				break;
 #define OP_hop2(vec, op) ((vec)[0] op (vec)[1])
 #define OP_hop3(vec, op) ((vec)[0] op (vec)[1] op (vec)[2])
 #define OP_hop4(vec, op) ((vec)[0] op (vec)[1] op (vec)[2] op (vec)[3])
@@ -2843,8 +2849,7 @@ pr_exec_ruamoko (progs_t *pr, int exitdepth)
 				switch (st->b) {
 #include "libs/gamecode/pr_hops.cinc"
 					default:
-						PR_RunError (pr, "invalid hops code: %04o",
-									 st->b);
+						PR_RunError (pr, "invalid hops code: %04o", st->b);
 				}
 				break;
 			default:
diff --git a/libs/gamecode/test/Makemodule.am b/libs/gamecode/test/Makemodule.am
index 2cfd9fbf9..dfccd91ae 100644
--- a/libs/gamecode/test/Makemodule.am
+++ b/libs/gamecode/test/Makemodule.am
@@ -11,6 +11,7 @@ libs_gamecode_tests = \
 	libs/gamecode/test/test-conv6 \
 	libs/gamecode/test/test-conv7 \
 	libs/gamecode/test/test-double \
+	libs/gamecode/test/test-extend \
 	libs/gamecode/test/test-float \
 	libs/gamecode/test/test-hops \
 	libs/gamecode/test/test-int \
@@ -101,6 +102,11 @@ libs_gamecode_test_test_double_SOURCES= \
 libs_gamecode_test_test_double_LDADD=		$(test_gamecode_libs)
 libs_gamecode_test_test_double_DEPENDENCIES=$(test_gamecode_libs)
 
+libs_gamecode_test_test_extend_SOURCES= \
+	libs/gamecode/test/test-extend.c
+libs_gamecode_test_test_extend_LDADD=			$(test_gamecode_libs)
+libs_gamecode_test_test_extend_DEPENDENCIES=	$(test_gamecode_libs)
+
 libs_gamecode_test_test_float_SOURCES= \
 	libs/gamecode/test/test-float.c
 libs_gamecode_test_test_float_LDADD=		$(test_gamecode_libs)
diff --git a/libs/gamecode/test/test-extend.c b/libs/gamecode/test/test-extend.c
new file mode 100644
index 000000000..bd05ab394
--- /dev/null
+++ b/libs/gamecode/test/test-extend.c
@@ -0,0 +1,223 @@
+#include "head.c"
+
+#include "QF/mathlib.h"
+
+#define _ -6.259853398707798e+18	// 0xdeadbeef
+
+static pr_vec4_t float_extend_init[] = {
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ 2, 3, 4, 5 },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+};
+
+static pr_vec4_t float_extend_expect[] = {
+	{ 5,  0,  _,  _ },
+	{ 4,  0,  0,  _ },
+	{ 3,  0,  0,  0 },
+	{ 4,  5,  0,  _ },
+	{ 2,  3,  0,  0 },
+	{ 3,  4,  5,  0 },
+	{ 2,  3,  4,  5 },
+	{ _,  _,  4,  1 },
+	{ _,  3,  1,  1 },
+	{ 2,  1,  1,  1 },
+	{ _,  4,  5,  1 },
+	{ 2,  3,  1,  1 },
+	{ 2,  3,  4,  1 },
+	{ _,  _,  _,  _ },
+	{ 5,  5,  _,  _ },
+	{ 4,  4,  4,  _ },
+	{ 3,  3,  3,  3 },
+	{ 4,  5,  0,  _ },
+	{ 2,  3,  2,  3 },
+	{ 3,  4,  5,  0 },
+	{ _,  _,  _,  _ },
+	{ _,  _,  4, -1 },
+	{ _,  3, -1, -1 },
+	{ 2, -1, -1, -1 },
+	{ _,  4,  5, -1 },
+	{ 2,  3, -1, -1 },
+	{ 2,  3,  4, -1 },
+	{ _,  _,  _,  _ },
+};
+
+static dstatement_t float_extend_statements[] = {
+	{ OP(0, 0, 0, OP_WITH), 0,  0, 0 },
+	{ OP(0, 0, 0, OP_WITH), 0, 28, 1 },
+	{ OP(0, 0, 0, OP_WITH), 0, 56, 2 },
+	{ OP(0, 0, 0, OP_WITH), 0, 84, 3 },
+
+	{ OP(0, 0, 0, OP_EXTEND), 27, 000,  0 },
+	{ OP(0, 0, 0, OP_EXTEND), 26, 001,  4 },
+	{ OP(0, 0, 0, OP_EXTEND), 25, 002,  8 },
+	{ OP(0, 0, 0, OP_EXTEND), 26, 003, 12 },
+	{ OP(0, 0, 0, OP_EXTEND), 24, 004, 16 },
+	{ OP(0, 0, 0, OP_EXTEND), 25, 005, 20 },
+
+	{ OP(0, 0, 1, OP_EXTEND), 26, 010,  2 },
+	{ OP(0, 0, 1, OP_EXTEND), 25, 011,  5 },
+	{ OP(0, 0, 1, OP_EXTEND), 24, 012,  8 },
+	{ OP(0, 0, 1, OP_EXTEND), 26, 013, 13 },
+	{ OP(0, 0, 1, OP_EXTEND), 24, 014, 16 },
+	{ OP(0, 0, 1, OP_EXTEND), 24, 015, 20 },
+
+	{ OP(0, 0, 2, OP_EXTEND), 27, 020,  0 },
+	{ OP(0, 0, 2, OP_EXTEND), 26, 021,  4 },
+	{ OP(0, 0, 2, OP_EXTEND), 25, 022,  8 },
+	{ OP(0, 0, 2, OP_EXTEND), 26, 023, 12 },
+	{ OP(0, 0, 2, OP_EXTEND), 24, 024, 16 },
+	{ OP(0, 0, 2, OP_EXTEND), 25, 025, 20 },
+
+	{ OP(0, 0, 3, OP_EXTEND), 26, 030,  2 },
+	{ OP(0, 0, 3, OP_EXTEND), 25, 031,  5 },
+	{ OP(0, 0, 3, OP_EXTEND), 24, 032,  8 },
+	{ OP(0, 0, 3, OP_EXTEND), 26, 033, 13 },
+	{ OP(0, 0, 3, OP_EXTEND), 24, 034, 16 },
+	{ OP(0, 0, 3, OP_EXTEND), 24, 035, 20 },
+};
+
+#undef _
+#define _ -1.1885959257070704e+148	// 0xdeadbeefdeadbeef
+
+static pr_dvec4_t double_extend_init[] = {
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ 2, 3, 4, 5 },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+	{ _, _, _, _ },
+};
+
+static pr_dvec4_t double_extend_expect[] = {
+	{ 5,  0,  _,  _ },
+	{ 4,  0,  0,  _ },
+	{ 3,  0,  0,  0 },
+	{ 4,  5,  0,  _ },
+	{ 2,  3,  0,  0 },
+	{ 3,  4,  5,  0 },
+	{ 2,  3,  4,  5 },
+	{ _,  _,  4,  1 },
+	{ _,  3,  1,  1 },
+	{ 2,  1,  1,  1 },
+	{ _,  4,  5,  1 },
+	{ 2,  3,  1,  1 },
+	{ 2,  3,  4,  1 },
+	{ _,  _,  _,  _ },
+	{ 5,  5,  _,  _ },
+	{ 4,  4,  4,  _ },
+	{ 3,  3,  3,  3 },
+	{ 4,  5,  0,  _ },
+	{ 2,  3,  2,  3 },
+	{ 3,  4,  5,  0 },
+	{ _,  _,  _,  _ },
+	{ _,  _,  4, -1 },
+	{ _,  3, -1, -1 },
+	{ 2, -1, -1, -1 },
+	{ _,  4,  5, -1 },
+	{ 2,  3, -1, -1 },
+	{ 2,  3,  4, -1 },
+	{ _,  _,  _,  _ },
+};
+
+static dstatement_t double_extend_statements[] = {
+	{ OP(0, 0, 0, OP_WITH), 0,   0, 0 },
+	{ OP(0, 0, 0, OP_WITH), 0,  56, 1 },
+	{ OP(0, 0, 0, OP_WITH), 0, 112, 2 },
+	{ OP(0, 0, 0, OP_WITH), 0, 168, 3 },
+
+	{ OP(0, 0, 0, OP_EXTEND), 54, 040,  0 },
+	{ OP(0, 0, 0, OP_EXTEND), 52, 041,  8 },
+	{ OP(0, 0, 0, OP_EXTEND), 50, 042, 16 },
+	{ OP(0, 0, 0, OP_EXTEND), 52, 043, 24 },
+	{ OP(0, 0, 0, OP_EXTEND), 48, 044, 32 },
+	{ OP(0, 0, 0, OP_EXTEND), 50, 045, 40 },
+
+	{ OP(0, 0, 1, OP_EXTEND), 52, 050,  4 },
+	{ OP(0, 0, 1, OP_EXTEND), 50, 051, 10 },
+	{ OP(0, 0, 1, OP_EXTEND), 48, 052, 16 },
+	{ OP(0, 0, 1, OP_EXTEND), 52, 053, 26 },
+	{ OP(0, 0, 1, OP_EXTEND), 48, 054, 32 },
+	{ OP(0, 0, 1, OP_EXTEND), 48, 055, 40 },
+
+	{ OP(0, 0, 2, OP_EXTEND), 54, 060,  0 },
+	{ OP(0, 0, 2, OP_EXTEND), 52, 061,  8 },
+	{ OP(0, 0, 2, OP_EXTEND), 50, 062, 16 },
+	{ OP(0, 0, 2, OP_EXTEND), 52, 063, 24 },
+	{ OP(0, 0, 2, OP_EXTEND), 48, 064, 32 },
+	{ OP(0, 0, 2, OP_EXTEND), 50, 065, 40 },
+
+	{ OP(0, 0, 3, OP_EXTEND), 52, 070,  4 },
+	{ OP(0, 0, 3, OP_EXTEND), 50, 071, 10 },
+	{ OP(0, 0, 3, OP_EXTEND), 48, 072, 16 },
+	{ OP(0, 0, 3, OP_EXTEND), 52, 073, 26 },
+	{ OP(0, 0, 3, OP_EXTEND), 48, 074, 32 },
+	{ OP(0, 0, 3, OP_EXTEND), 48, 075, 40 },
+};
+
+test_t tests[] = {
+	{
+		.desc = "float extend",
+		.num_globals = num_globals(float_extend_init,float_extend_expect),
+		.num_statements = num_statements (float_extend_statements),
+		.statements = float_extend_statements,
+		.init_globals = (pr_int_t *) float_extend_init,
+		.expect_globals = (pr_int_t *) float_extend_expect,
+	},
+	{
+		.desc = "double extend",
+		.num_globals = num_globals(double_extend_init,double_extend_expect),
+		.num_statements = num_statements (double_extend_statements),
+		.statements = double_extend_statements,
+		.init_globals = (pr_int_t *) double_extend_init,
+		.expect_globals = (pr_int_t *) double_extend_expect,
+	},
+};
+
+#include "main.c"