diff --git a/zap/src/config.rs b/zap/src/config.rs
index 89ae3a30..0bcd0428 100644
--- a/zap/src/config.rs
+++ b/zap/src/config.rs
@@ -426,6 +426,10 @@ impl Range {
 			None
 		}
 	}
+
+	pub fn numty(&self) -> Option<NumTy> {
+		Some(NumTy::from_f64(self.min.unwrap_or(0.0), self.max?))
+	}
 }
 
 impl Display for Range {
diff --git a/zap/src/irgen/des.rs b/zap/src/irgen/des.rs
index 47b16c2b..bad52256 100644
--- a/zap/src/irgen/des.rs
+++ b/zap/src/irgen/des.rs
@@ -101,7 +101,10 @@ impl Des<'_> {
 				} else {
 					let (len_name, len_expr) = self.add_occurrence("len");
 
-					self.push_local(len_name.clone(), Some(self.readnumty(NumTy::U16)));
+					self.push_local(
+						len_name.clone(),
+						Some(self.readnumty(range.numty().unwrap_or(NumTy::U16))),
+					);
 
 					if self.checks {
 						self.push_range_check(len_expr.clone(), *range);
@@ -116,7 +119,10 @@ impl Des<'_> {
 					self.push_read_copy(into, len.into());
 				} else {
 					let (len_name, len_expr) = self.add_occurrence("len");
-					self.push_local(len_name.clone(), Some(self.readnumty(NumTy::U16)));
+					self.push_local(
+						len_name.clone(),
+						Some(self.readnumty(range.numty().unwrap_or(NumTy::U16))),
+					);
 
 					if self.checks {
 						self.push_range_check(len_expr.clone(), *range);
@@ -143,7 +149,10 @@ impl Des<'_> {
 				} else {
 					let (len_name, len_expr) = self.add_occurrence("len");
 
-					self.push_local(len_name.clone(), Some(self.readnumty(NumTy::U16)));
+					self.push_local(
+						len_name.clone(),
+						Some(self.readnumty(range.numty().unwrap_or(NumTy::U16))),
+					);
 
 					if self.checks {
 						self.push_range_check(len_expr.clone(), *range);
diff --git a/zap/src/irgen/ser.rs b/zap/src/irgen/ser.rs
index 8abaa7aa..b2917e7e 100644
--- a/zap/src/irgen/ser.rs
+++ b/zap/src/irgen/ser.rs
@@ -110,7 +110,7 @@ impl Ser<'_> {
 						self.push_range_check(len_expr.clone(), *range);
 					}
 
-					self.push_writeu16(len_expr.clone());
+					self.push_writenumty(len_expr.clone(), range.numty().unwrap_or(NumTy::U16));
 					self.push_writestring(from_expr, len_expr.clone());
 				}
 			}
@@ -133,7 +133,7 @@ impl Ser<'_> {
 						self.push_range_check(len_expr.clone(), *range);
 					}
 
-					self.push_writeu16(len_expr.clone());
+					self.push_writenumty(len_expr.clone(), range.numty().unwrap_or(NumTy::U16));
 					self.push_write_copy(from_expr, len_name.as_str().into())
 				}
 			}
@@ -162,7 +162,7 @@ impl Ser<'_> {
 						self.push_range_check(len_expr.clone(), *range);
 					}
 
-					self.push_writeu16(len_expr.clone());
+					self.push_writenumty(len_expr.clone(), range.numty().unwrap_or(NumTy::U16));
 
 					self.push_stmt(Stmt::NumFor {
 						var: var_name.clone(),