diff --git a/src/llvm_backend_expr.cpp b/src/llvm_backend_expr.cpp
index 2ef7f9b29..63c45711f 100644
--- a/src/llvm_backend_expr.cpp
+++ b/src/llvm_backend_expr.cpp
@@ -2546,7 +2546,9 @@ gb_internal lbValue lb_emit_conv(lbProcedure *p, lbValue value, Type *t) {
 			lbValue res_i128 = lb_emit_runtime_call(p, call, args);
 			return lb_emit_conv(p, res_i128, t);
 		}
-		i64 sz = type_size_of(src);
+		// the intermediate int must be at least as wide as the dest,
+		// otherwise e.g. f32 -> u64 truncates through a 32-bit fptoui
+		i64 sz = gb_max(type_size_of(src), type_size_of(dst));
 
 		lbValue res = {};
 		res.type = t;