diff --git a/src/compiler/sema_expr.c b/src/compiler/sema_expr.c
index f87a437ac..562f8da0b 100644
--- a/src/compiler/sema_expr.c
+++ b/src/compiler/sema_expr.c
@@ -5951,8 +5951,9 @@ SLICE_COPY:;
 	Range *left_range = &left->slice_expr.range;
 	IndexDiff left_len = range_const_len(left_range);
 	IndexDiff right_len = 0;
-	if (!expr_is_const_slice(right))
+	if (!expr_is_const(right))
 	{
+		ASSERT_SPAN(right, right->expr_kind == EXPR_SLICE);
 		Range *right_range = &right->slice_expr.range;
 		right_len = range_const_len(right_range);
 	}
@@ -5960,10 +5961,10 @@ SLICE_COPY:;
 	{
 		right_len = sema_len_from_const(right);
 	}
-		if (left_len >= 0 && right_len >= 0 && left_len != right_len)
-		{
-			RETURN_SEMA_ERROR(expr, "Length mismatch between slices.");
-		}
+	if (left_len >= 0 && right_len >= 0 && left_len != right_len)
+	{
+		RETURN_SEMA_ERROR(expr, "Length mismatch between slices.");
+	}
 	expr->expr_kind = EXPR_SLICE_COPY;
 	expr->type = left->type;
 	expr->slice_assign_expr.left = exprid(left);
diff --git a/test/test_suite/slices/slice_copy.c3t b/test/test_suite/slices/slice_copy.c3t
new file mode 100644
index 000000000..2e1ab6308
--- /dev/null
+++ b/test/test_suite/slices/slice_copy.c3t
@@ -0,0 +1,103 @@
+// #target: macos-x64
+// #safe: yes
+module test;
+
+fn int main()
+{
+	const FOO = "FOO";
+	String str;
+	str[:FOO.len] = FOO[..];
+	return 0;
+}
+
+/* #expect: test.ll
+
+define i32 @main() #0 {
+entry:
+  %str = alloca %"char[]", align 8
+  %taddr = alloca i64, align 8
+  %taddr1 = alloca i64, align 8
+  %varargslots = alloca [2 x %any], align 16
+  %indirectarg = alloca %"any[]", align 8
+  %taddr3 = alloca i64, align 8
+  %taddr4 = alloca i64, align 8
+  %varargslots5 = alloca [2 x %any], align 16
+  %indirectarg8 = alloca %"any[]", align 8
+  %taddr11 = alloca i64, align 8
+  %taddr12 = alloca i64, align 8
+  %varargslots13 = alloca [2 x %any], align 16
+  %indirectarg16 = alloca %"any[]", align 8
+  call void @llvm.memset.p0.i64(ptr align 8 %str, i8 0, i64 16, i1 false)
+  %0 = load %"char[]", ptr %str, align 8
+  %1 = extractvalue %"char[]" %0, 0
+  %2 = extractvalue %"char[]" %0, 1
+  %gt = icmp sgt i64 0, %2
+  %3 = call i1 @llvm.expect.i1(i1 %gt, i1 false)
+  br i1 %3, label %panic, label %checkok
+
+checkok:                                          ; preds = %entry
+  %lt = icmp slt i64 %2, 3
+  %4 = call i1 @llvm.expect.i1(i1 %lt, i1 false)
+  br i1 %4, label %panic2, label %checkok9
+
+checkok9:                                         ; preds = %checkok
+  %5 = insertvalue %"char[]" undef, ptr %1, 0
+  %6 = insertvalue %"char[]" %5, i64 3, 1
+  %7 = extractvalue %"char[]" %6, 0
+  %8 = extractvalue %"char[]" %6, 1
+  %neq = icmp ne i64 %8, 3
+  %9 = call i1 @llvm.expect.i1(i1 %neq, i1 false)
+  br i1 %9, label %panic10, label %checkok17
+
+checkok17:                                        ; preds = %checkok9
+  call void @llvm.memmove.p0.p0.i64(ptr align 1 %7, ptr align 1 @.str.1, i64 3, i1 false)
+  ret i32 0
+
+panic:                                            ; preds = %entry
+  store i64 %2, ptr %taddr, align 8
+  %10 = insertvalue %any undef, ptr %taddr, 0
+  %11 = insertvalue %any %10, i64 ptrtoint (ptr @"$ct.long" to i64), 1
+  store i64 0, ptr %taddr1, align 8
+  %12 = insertvalue %any undef, ptr %taddr1, 0
+  %13 = insertvalue %any %12, i64 ptrtoint (ptr @"$ct.long" to i64), 1
+  store %any %11, ptr %varargslots, align 16
+  %ptradd = getelementptr inbounds i8, ptr %varargslots, i64 16
+  store %any %13, ptr %ptradd, align 16
+  %14 = insertvalue %"any[]" undef, ptr %varargslots, 0
+  %"$$temp" = insertvalue %"any[]" %14, i64 2, 1
+  store %"any[]" %"$$temp", ptr %indirectarg, align 8
+  call void @std.core.builtin.panicf(ptr @.panic_msg, i64 61, ptr @.file, i64 13, ptr @.func, i64 4, i32 7, ptr byval(%"any[]") align 8 %indirectarg) #4
+  unreachable
+
+panic2:                                           ; preds = %checkok
+  store i64 2, ptr %taddr3, align 8
+  %15 = insertvalue %any undef, ptr %taddr3, 0
+  %16 = insertvalue %any %15, i64 ptrtoint (ptr @"$ct.long" to i64), 1
+  store i64 %2, ptr %taddr4, align 8
+  %17 = insertvalue %any undef, ptr %taddr4, 0
+  %18 = insertvalue %any %17, i64 ptrtoint (ptr @"$ct.long" to i64), 1
+  store %any %16, ptr %varargslots5, align 16
+  %ptradd6 = getelementptr inbounds i8, ptr %varargslots5, i64 16
+  store %any %18, ptr %ptradd6, align 16
+  %19 = insertvalue %"any[]" undef, ptr %varargslots5, 0
+  %"$$temp7" = insertvalue %"any[]" %19, i64 2, 1
+  store %"any[]" %"$$temp7", ptr %indirectarg8, align 8
+  call void @std.core.builtin.panicf(ptr @.panic_msg.2, i64 60, ptr @.file, i64 13, ptr @.func, i64 4, i32 7, ptr byval(%"any[]") align 8 %indirectarg8) #4
+  unreachable
+
+panic10:                                          ; preds = %checkok9
+  store i64 %8, ptr %taddr11, align 8
+  %20 = insertvalue %any undef, ptr %taddr11, 0
+  %21 = insertvalue %any %20, i64 ptrtoint (ptr @"$ct.ulong" to i64), 1
+  store i64 3, ptr %taddr12, align 8
+  %22 = insertvalue %any undef, ptr %taddr12, 0
+  %23 = insertvalue %any %22, i64 ptrtoint (ptr @"$ct.ulong" to i64), 1
+  store %any %21, ptr %varargslots13, align 16
+  %ptradd14 = getelementptr inbounds i8, ptr %varargslots13, i64 16
+  store %any %23, ptr %ptradd14, align 16
+  %24 = insertvalue %"any[]" undef, ptr %varargslots13, 0
+  %"$$temp15" = insertvalue %"any[]" %24, i64 2, 1
+  store %"any[]" %"$$temp15", ptr %indirectarg16, align 8
+  call void @std.core.builtin.panicf(ptr @.panic_msg.3, i64 38, ptr @.file, i64 13, ptr @.func, i64 4, i32 7, ptr byval(%"any[]") align 8 %indirectarg16) #4
+  unreachable
+}