diff --git a/compiler/aasmtai.pas b/compiler/aasmtai.pas
index 4ce1572fa2..bf60d3587b 100644
--- a/compiler/aasmtai.pas
+++ b/compiler/aasmtai.pas
@@ -653,6 +653,9 @@ interface
           symofs,
           value   : int64;
           consttype : taiconst_type;
+          { sleb128 and uleb128 values have a varying length, by calling FixSize their size can be fixed
+            to avoid that other offsets need to be changed. The value to write is stored in fixed_size }
+          fixed_size : byte;
           { we use for the 128bit int64/qword for now because I can't imagine a
             case where we need 128 bit now (FK) }
           constructor Create(_typ:taiconst_type;_value : int64);
@@ -707,6 +710,9 @@ interface
           procedure derefimpl;override;
           function getcopy:tlinkedlistitem;override;
           function size:longint;
+          { sleb128 and uleb128 values have a varying length, by calling FixSize their size can be fixed
+            to avoid that other offsets need to be changed. The value to write is stored in fixed_size }
+          Procedure FixSize;
        end;
 
        { floating point const }
@@ -2002,9 +2008,31 @@ implementation
             else
               result:=sizeof(pint);
           aitconst_uleb128bit :
-            result:=LengthUleb128(qword(value));
+            begin
+              if fixed_size>0 then
+                result:=fixed_size
+              else if sym=nil then
+                begin
+                  FixSize;
+                  result:=fixed_size;
+                end
+              else
+                { worst case }
+                result:=sizeof(pint)+2;
+            end;
           aitconst_sleb128bit :
-            result:=LengthSleb128(value);
+            begin
+              if fixed_size>0 then
+                result:=fixed_size
+              else if sym=nil then
+                begin
+                  FixSize;
+                  result:=fixed_size;
+                end
+              else
+                { worst case }
+                result:=sizeof(pint)+2;
+            end;
           aitconst_half16bit,
           aitconst_gs:
             result:=2;
@@ -2024,6 +2052,19 @@ implementation
       end;
 
 
+    procedure tai_const.FixSize;
+      begin
+        case consttype of
+          aitconst_uleb128bit:
+            fixed_size:=LengthUleb128(qword(value));
+          aitconst_sleb128bit:
+            fixed_size:=LengthSleb128(value);
+          else
+            Internalerror(2019030301);
+        end;
+      end;
+
+
 {****************************************************************************
                                TAI_realconst
  ****************************************************************************}
diff --git a/compiler/aggas.pas b/compiler/aggas.pas
index 2cdc826645..8b0cd7579e 100644
--- a/compiler/aggas.pas
+++ b/compiler/aggas.pas
@@ -1,4 +1,4 @@
-{
+  {
     Copyright (c) 1998-2006 by the Free Pascal team
 
     This unit implements the generic part of the GNU assembler
@@ -586,7 +586,7 @@ implementation
         i,len : longint;
         buf   : array[0..63] of byte;
       begin
-        len:=EncodeUleb128(a,buf);
+        len:=EncodeUleb128(a,buf,0);
         for i:=0 to len-1 do
           begin
             if (i > 0) then
@@ -634,7 +634,7 @@ implementation
         i,len : longint;
         buf   : array[0..255] of byte;
       begin
-        len:=EncodeSleb128(a,buf);
+        len:=EncodeSleb128(a,buf,0);
         for i:=0 to len-1 do
           begin
             if (i > 0) then
diff --git a/compiler/assemble.pas b/compiler/assemble.pas
index 1d5a7320a7..892c38e4a1 100644
--- a/compiler/assemble.pas
+++ b/compiler/assemble.pas
@@ -1767,6 +1767,8 @@ Implementation
                      else
                        Tai_const(hp).value:=objsymend.address-objsym.address+Tai_const(hp).symofs;
                    end;
+                 if (Tai_const(hp).consttype in [aitconst_uleb128bit,aitconst_sleb128bit]) then
+                   Tai_const(hp).fixsize;
                  ObjData.alloc(tai_const(hp).size);
                end;
              ait_section:
@@ -2035,11 +2037,13 @@ Implementation
                    aitconst_uleb128bit,
                    aitconst_sleb128bit :
                      begin
+                       if Tai_const(hp).fixed_size=0 then
+                         Internalerror(2019030302);
                        if tai_const(hp).consttype=aitconst_uleb128bit then
-                         leblen:=EncodeUleb128(qword(Tai_const(hp).value),lebbuf)
+                         leblen:=EncodeUleb128(qword(Tai_const(hp).value),lebbuf,Tai_const(hp).fixed_size)
                        else
-                         leblen:=EncodeSleb128(Tai_const(hp).value,lebbuf);
-                       if leblen<>tai_const(hp).size then
+                         leblen:=EncodeSleb128(Tai_const(hp).value,lebbuf,Tai_const(hp).fixed_size);
+                       if leblen<>tai_const(hp).fixed_size then
                          internalerror(200709271);
                        ObjData.writebytes(lebbuf,leblen);
                      end;
diff --git a/compiler/cutils.pas b/compiler/cutils.pas
index 5978828aca..415dd3e867 100644
--- a/compiler/cutils.pas
+++ b/compiler/cutils.pas
@@ -182,8 +182,8 @@ interface
 
     function LengthUleb128(a: qword) : byte;
     function LengthSleb128(a: int64) : byte;
-    function EncodeUleb128(a: qword;out buf) : byte;
-    function EncodeSleb128(a: int64;out buf) : byte;
+    function EncodeUleb128(a: qword;out buf;len: byte) : byte;
+    function EncodeSleb128(a: int64;out buf;len: byte) : byte;
 
   { hide Sysutils.ExecuteProcess in units using this one after SysUtils}
   const
@@ -1672,7 +1672,7 @@ implementation
       end;
 
 
-    function EncodeUleb128(a: qword;out buf) : byte;
+    function EncodeUleb128(a: qword;out buf;len : byte) : byte;
       var
         b: byte;
         pbuf : pbyte;
@@ -1687,13 +1687,13 @@ implementation
           pbuf^:=b;
           inc(pbuf);
           inc(result);
-          if a=0 then
+          if (a=0) and  (result>=len) then
             break;
         until false;
       end;
 
 
-    function EncodeSleb128(a: int64;out buf) : byte;
+    function EncodeSleb128(a: int64;out buf;len : byte) : byte;
       var
         b, size: byte;
         more: boolean;
@@ -1707,7 +1707,7 @@ implementation
           b := a and $7f;
           a := SarInt64(a, 7);
 
-          if (
+          if (result+1>=len) and (
             ((a = 0) and (b and $40 = 0)) or
             ((a = -1) and (b and $40 <> 0))
           ) then