diff --git a/compiler/jsgen.nim b/compiler/jsgen.nim
index 8abb830bd2..fd8ef583d0 100644
--- a/compiler/jsgen.nim
+++ b/compiler/jsgen.nim
@@ -2333,8 +2333,8 @@ proc genMagic(p: PProc, n: PNode, r: var TCompRes) =
       r.res = "if (null != $1) { if (null == $2) $2 = $3; else $2 += $3; }" %
         [b, lhs.rdLoc, tmp]
     else:
-      let (a, tmp) = maybeMakeTemp(p, n[1], lhs)
-      r.res = "$1.push.apply($3, $2);" % [a, rhs.rdLoc, tmp]
+      useMagic(p, "nimAddStrStr")
+      r.res = "nimAddStrStr($1, $2);" % [lhs.rdLoc, rhs.rdLoc]
     r.kind = resExpr
   of mAppendSeqElem:
     var x, y: TCompRes = default(TCompRes)
diff --git a/lib/system/jssys.nim b/lib/system/jssys.nim
index 6934e67ee4..b469c4695f 100644
--- a/lib/system/jssys.nim
+++ b/lib/system/jssys.nim
@@ -687,6 +687,14 @@ proc isObj(obj, subclass: PNimType): bool {.compilerproc.} =
 proc addChar(x: string, c: char) {.compilerproc, asmNoStackFrame.} =
   {.emit: "`x`.push(`c`);".}
 
+proc nimAddStrStr(x, y: string) {.compilerproc, asmNoStackFrame.} =
+  {.emit: """
+  var L = `y`.length;
+  for (var i = 0; i < L; ++i) {
+    `x`.push(`y`[i]);
+  }
+  """.}
+
 {.pop.}
 
 proc tenToThePowerOf(b: int): BiggestFloat =
diff --git a/tests/system/tconcat.nim b/tests/system/tconcat.nim
index fdce3ea00d..8cf995c938 100644
--- a/tests/system/tconcat.nim
+++ b/tests/system/tconcat.nim
@@ -1,11 +1,33 @@
 discard """
-  output: "DabcD"
+  targets: "c cpp js"
+  output: '''
+DabcD
+(8192, 8, 1024)
+'''
 """
 
-const
-  x = "abc"
+import std/assertions
 
-var v = "D" & x & "D"
+block:
+  const
+    x = "abc"
 
-echo v
+  var v = "D" & x & "D"
 
+  doAssert v == "DabcD"
+  echo v
+
+block: # test large additions
+  var a = "abcdefgh"
+  let initialLen = a.len
+  let times = 10
+  for i in 1..times:
+    let start = a.len
+    a.add(a)
+    doAssert a.len == 2 * start
+  let multiplier = 1 shl times
+  doAssert a.len == initialLen * multiplier
+  echo (a.len, initialLen, multiplier)
+  for i in 1 ..< multiplier:
+    for j in 0 ..< initialLen:
+      doAssert a[j] == a[i * initialLen + j]