diff --git a/Source/exehead/Ui.c b/Source/exehead/Ui.c
index f7ff7f60..4414b2d1 100644
--- a/Source/exehead/Ui.c
+++ b/Source/exehead/Ui.c
@@ -780,14 +780,20 @@ static BOOL CALLBACK UninstProc(HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM l
 #endif
 
 
-static void NSISCALL SetSizeText(int dlgItem, int prefix, unsigned kb)
+static void NSISCALL SetSizeText(int dlgItem, int prefix, unsigned kb, int roundUp)
 {
   char scalestr[32], byte[32];
   unsigned sh=20;
   int scale=LANG_GIGA;
-  
+
+  if (kb < 1024*1024) { sh=10; scale=LANG_MEGA; }
   if (kb < 1024) { sh=0; scale=LANG_KILO; }
-  else if (kb < 1024*1024) { sh=10; scale=LANG_MEGA; }
+
+  if (roundUp)
+    // this will not overflow because currently, installers
+    // can't contain over 2GB of data and this is not used
+    // for the available size, but only required size
+    kb += (1 << sh) / 10; // round up number after decimal point
 
   wsprintf(
     GetNSISString(g_tmp,prefix)+mystrlen(g_tmp),
@@ -959,9 +965,9 @@ static BOOL CALLBACK DirProc(HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPar
       error = NSIS_INSTDIR_NOT_ENOUGH_SPACE;
 
     if (LANG_STR_TAB(LANG_SPACE_REQ)) {
-      SetSizeText(IDC_SPACEREQUIRED,LANG_SPACE_REQ,total);
+      SetSizeText(IDC_SPACEREQUIRED,LANG_SPACE_REQ,total,1);
       if (available_set)
-        SetSizeText(IDC_SPACEAVAILABLE,LANG_SPACE_AVAIL,available);
+        SetSizeText(IDC_SPACEAVAILABLE,LANG_SPACE_AVAIL,available,0);
       else
         SetUITextNT(IDC_SPACEAVAILABLE,"");
     }
@@ -1354,7 +1360,7 @@ static BOOL CALLBACK SelProc(HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPar
     RefreshComponents(hwndTree1, hTreeItems);
 
     if (LANG_STR_TAB(LANG_SPACE_REQ)) {
-      SetSizeText(IDC_SPACEREQUIRED,LANG_SPACE_REQ,sumsecsfield(size_kb));
+      SetSizeText(IDC_SPACEREQUIRED,LANG_SPACE_REQ,sumsecsfield(size_kb),1);
     }
   }