diff --git a/README.md b/README.md
index 5f75c82..2fbf8a4 100644
--- a/README.md
+++ b/README.md
@@ -221,12 +221,14 @@ Vnlike many other programming languages with modules, the modules in `CENTVRION`
 ### FORS
 ![CVM FORS](snippets/fors.png)
 
-The `FORS` module allows you to add randomness to your `CENTVRION` program. It adds 2 new built-in functions: `FORTIS_NVMERVS int int` and `FORTIS_ELECTIONIS ['a]`.
+The `FORS` module allows you to add randomness to your `CENTVRION` program. It adds 3 new built-in functions: `FORTIS_NVMERVS int int`, `FORTIS_ELECTIONIS ['a]`, and `SEMEN int`.
 
 `FORTIS_NVMERVS int int` picks a random int in the (inclusive) range of the two given ints.
 
 `FORTIS_ELECTIONIS ['a]` picks a random element from the given array. `FORTIS_ELECTIONIS array` is identical to ```array[FORTIS_NVMERVS NVLLVS ((LONGITVDO array)-I)]```.
 
+`SEMEN int` seeds the random number generator for reproducibility.
+
 ### FRACTIO
 ![CVM FRACTIO](snippets/fractio.png)
 
diff --git a/centvrion/ast_nodes.py b/centvrion/ast_nodes.py
index f9ffb6d..c55fb0a 100644
--- a/centvrion/ast_nodes.py
+++ b/centvrion/ast_nodes.py
@@ -920,6 +920,14 @@ class BuiltIn(Node):
         if len(lst) == 0:
           raise CentvrionError("FORTIS_ELECTIONIS: cannot select from an empty array")
         return vtable, lst[random.randint(0, len(lst) - 1)]
+      case "SEMEN":
+        if "FORS" not in vtable["#modules"]:
+          raise CentvrionError("Cannot use 'SEMEN' without module 'FORS'")
+        seed = params[0].value()
+        if not isinstance(seed, int):
+          raise CentvrionError("SEMEN requires an integer seed")
+        random.seed(seed)
+        return vtable, ValNul()
       case "LONGITVDO":
         if isinstance(params[0], (ValList, ValStr)):
           return vtable, ValInt(len(params[0].value()))
diff --git a/centvrion/compiler/emit_expr.py b/centvrion/compiler/emit_expr.py
index fe2b433..84dc9a6 100644
--- a/centvrion/compiler/emit_expr.py
+++ b/centvrion/compiler/emit_expr.py
@@ -186,6 +186,14 @@ def _emit_builtin(node, ctx):
       else:
         lines.append(f"CentValue {tmp} = cent_fortis_electionis({param_vars[0]});")
 
+    case "SEMEN":
+      if not ctx.has_module("FORS"):
+        lines.append('cent_runtime_error("FORS module required for SEMEN");')
+        lines.append(f"CentValue {tmp} = cent_null();")
+      else:
+        lines.append(f"cent_semen({param_vars[0]});")
+        lines.append(f"CentValue {tmp} = cent_null();")
+
     case "ERVMPE":
       # break as expression (side-effecting; result is unused)
       lines.append("break;")
diff --git a/centvrion/compiler/runtime/cent_runtime.c b/centvrion/compiler/runtime/cent_runtime.c
index 553bd10..2a28084 100644
--- a/centvrion/compiler/runtime/cent_runtime.c
+++ b/centvrion/compiler/runtime/cent_runtime.c
@@ -533,6 +533,12 @@ CentValue cent_fortis_electionis(CentValue lst) {
   return lst.lval.items[rand() % lst.lval.len];
 }
 
+void cent_semen(CentValue seed) {
+  if (seed.type != CENT_INT)
+    cent_type_error("'SEMEN' requires an integer seed");
+  srand((unsigned)seed.ival);
+}
+
 /* ------------------------------------------------------------------ */
 /* Array helpers                                                        */
 /* ------------------------------------------------------------------ */
diff --git a/centvrion/compiler/runtime/cent_runtime.h b/centvrion/compiler/runtime/cent_runtime.h
index 4612309..b37dbb4 100644
--- a/centvrion/compiler/runtime/cent_runtime.h
+++ b/centvrion/compiler/runtime/cent_runtime.h
@@ -177,6 +177,7 @@ CentValue cent_avdi_numerus(void);                    /* AVDI_NVMERVS */
 CentValue cent_longitudo(CentValue v);                  /* LONGITVDO  */
 CentValue cent_fortis_numerus(CentValue lo, CentValue hi); /* FORTIS_NVMERVS */
 CentValue cent_fortis_electionis(CentValue lst);          /* FORTIS_ELECTIONIS */
+void      cent_semen(CentValue seed);                          /* SEMEN */
 void      cent_everro(void);                                   /* EVERRO */
 
 /* ------------------------------------------------------------------ */
diff --git a/centvrion/lexer.py b/centvrion/lexer.py
index 6745a48..b441ffd 100644
--- a/centvrion/lexer.py
+++ b/centvrion/lexer.py
@@ -41,7 +41,8 @@ builtin_tokens = [("BUILTIN", i) for i in [
   "EVERRO",
   "FORTIS_NVMERVS",
   "FORTIS_ELECTIONIS",
-  "LONGITVDO"
+  "LONGITVDO",
+  "SEMEN"
 ]]
 
 data_tokens = [
diff --git a/snippets/syntaxes/centvrion.sublime-syntax b/snippets/syntaxes/centvrion.sublime-syntax
index 566e83d..0afa2ba 100644
--- a/snippets/syntaxes/centvrion.sublime-syntax
+++ b/snippets/syntaxes/centvrion.sublime-syntax
@@ -57,7 +57,7 @@ contexts:
       scope: constant.language.centvrion
 
   builtins:
-    - match: '\b(AVDI_NVMERVS|AVDI|DICE|FORTIS_NVMERVS|FORTIS_ELECTIONIS|LONGITVDO)\b'
+    - match: '\b(AVDI_NVMERVS|AVDI|DICE|FORTIS_NVMERVS|FORTIS_ELECTIONIS|LONGITVDO|SEMEN)\b'
       scope: support.function.builtin.centvrion
 
   modules:
diff --git a/tests.py b/tests.py
index ed7322e..582cd5a 100644
--- a/tests.py
+++ b/tests.py
@@ -460,6 +460,7 @@ builtin_tests = [
   ('LONGITVDO("salve")', Program([], [ExpressionStatement(BuiltIn("LONGITVDO", [String("salve")]))]), ValInt(5)),
   ('LONGITVDO("")', Program([], [ExpressionStatement(BuiltIn("LONGITVDO", [String("")]))]), ValInt(0)),
   ("CVM FORS\nFORTIS_ELECTIONIS([I, II, III])", Program([ModuleCall("FORS")], [ExpressionStatement(BuiltIn("FORTIS_ELECTIONIS", [DataArray([Numeral("I"), Numeral("II"), Numeral("III")])]))]), ValInt(1)),
+  ("CVM FORS\nSEMEN(XLII)\nFORTIS_NVMERVS(I, C)", Program([ModuleCall("FORS")], [ExpressionStatement(BuiltIn("SEMEN", [Numeral("XLII")])), ExpressionStatement(BuiltIn("FORTIS_NVMERVS", [Numeral("I"), Numeral("C")]))]), ValInt(82)),
 ]
 
 class TestBuiltins(unittest.TestCase):
@@ -494,6 +495,8 @@ error_tests = [
   ("\"hello\" MINVS \"world\"", CentvrionError),                       # comparison with strings
   ("I[I]", CentvrionError),                                           # indexing a non-array
   ("DESIGNA x VT I\nDESIGNA x[I] VT II", CentvrionError),             # index-assign to non-array
+  ("SEMEN(I)", CentvrionError),                                        # requires FORS module
+  ('CVM FORS\nSEMEN("abc")', CentvrionError),                          # SEMEN requires integer seed
   ("FORTIS_ELECTIONIS([])", CentvrionError),                           # FORS required for FORTIS_ELECTIONIS
   ("CVM FORS\nFORTIS_ELECTIONIS([])", CentvrionError),                 # FORTIS_ELECTIONIS on empty array
   ("CVM FORS\nFORTIS_NVMERVS(X, I)", CentvrionError),                  # FORTIS_NVMERVS a > b