diff --git a/components/fpdebug/fpdbgdwarfdataclasses.pas b/components/fpdebug/fpdbgdwarfdataclasses.pas
index 0937b78ac3..5b4be5e8c4 100644
--- a/components/fpdebug/fpdbgdwarfdataclasses.pas
+++ b/components/fpdebug/fpdbgdwarfdataclasses.pas
@@ -3551,7 +3551,8 @@ function TDWarfLineMap.GetAddressesForLine(ALine: Cardinal; var AResultList: TDB
   NoData: Boolean; AFindSibling: TGetLineAddrFindSibling; AFoundLine: PInteger;
   AMaxSiblingDistance: integer; ACU: TDwarfCompilationUnit): Boolean;
 var
-  idx, offset, Addr1, Addr2: TDBGPtr;
+  idx: integer;
+  offset, Addr1, Addr2: TDBGPtr;
   LineOffsets: Array of Byte;
   Addresses: Array of TDBGPtr;
   o: Byte;
@@ -3563,7 +3564,7 @@ begin
   offset := ALine mod 256;
   if idx >= Length(FLineIndexList) then begin
     if AFindSibling  = fsBefore then begin
-      idx := Length(FLineIndexList);
+      idx := Length(FLineIndexList)-1;
       offset := 255;
     end
     else
@@ -3606,7 +3607,15 @@ begin
           fsBefore: begin
               if i > 0 then begin
                 dec(i);
+                CurOffs := CurOffs - o;
                 offset := 0;  // found line before
+              end
+              else begin
+                // i=0 => will trigger continue for outer loop
+                dec(idx);
+                if idx < 0 then
+                  exit;
+                offset := 255; // Must be last entry from block before (if there is a block before)
               end;
             end;
           fsNext, fsNextFunc, fsNextFuncLazy: begin
@@ -3625,7 +3634,19 @@ begin
       break;
     case AFindSibling of
       fsNone: exit;
-      else    continue;
+      fsBefore: begin
+        if i = 0 then
+          continue;
+        assert(i=l, 'TDWarfLineMap.GetAddressesForLine: i=l');
+        dec(i);
+        break;
+      end;
+      else begin
+        inc(idx);
+        if idx >= Length(FLineIndexList) then
+          exit;
+        continue;
+      end;
     end;
   until False;
 
diff --git a/components/fpdebug/test/FpTest.lpi b/components/fpdebug/test/FpTest.lpi
index b68b98ec19..9a452274f2 100644
--- a/components/fpdebug/test/FpTest.lpi
+++ b/components/fpdebug/test/FpTest.lpi
@@ -63,7 +63,7 @@
         <PackageName Value="FCL"/>
       </Item5>
     </RequiredPackages>
-    <Units Count="10">
+    <Units Count="11">
       <Unit0>
         <Filename Value="FpTest.lpr"/>
         <IsPartOfProject Value="True"/>
@@ -113,6 +113,11 @@
         <IsPartOfProject Value="True"/>
         <UnitName Value="TestErrorHandler"/>
       </Unit9>
+      <Unit10>
+        <Filename Value="testlinemap.pas"/>
+        <IsPartOfProject Value="True"/>
+        <UnitName Value="TestLineMap"/>
+      </Unit10>
     </Units>
   </ProjectOptions>
   <CompilerOptions>
diff --git a/components/fpdebug/test/FpTest.lpr b/components/fpdebug/test/FpTest.lpr
index eba7c734e7..084e7d5439 100644
--- a/components/fpdebug/test/FpTest.lpr
+++ b/components/fpdebug/test/FpTest.lpr
@@ -5,7 +5,7 @@ program FpTest;
 uses
   Interfaces, Forms, GuiTestRunner, TestTypeInfo, TestHelperClasses, TestDwarfSetup1,
   TestDwarfSetupBasic, TestDwarfVarious, testdwarfsetupArray, TestMemManager, TestPascalParser,
-  TestErrorHandler;
+  TestErrorHandler, TestLineMap;
 
 {$R *.res}
 
diff --git a/components/fpdebug/test/testlinemap.pas b/components/fpdebug/test/testlinemap.pas
new file mode 100644
index 0000000000..e076b1f71a
--- /dev/null
+++ b/components/fpdebug/test/testlinemap.pas
@@ -0,0 +1,181 @@
+unit TestLineMap;
+
+{$mode objfpc}{$H+}
+
+interface
+
+uses
+  Classes, SysUtils, Math, FpDbgDwarfDataClasses, FpDbgInfo, DbgIntfBaseTypes, fpcunit, testutils,
+  testregistry;
+
+type
+
+  { TTestLineMap }
+
+  TTestLineMap = class(TTestCase)
+  private
+    LMap: TDWarfLineMap;
+
+    procedure InitMap(l: array of integer);
+    procedure CheckNotFound(ASearch: Integer; AFindSibling: TGetLineAddrFindSibling; AMaxSiblingDistance: integer = 0);
+    procedure CheckFound(ASearch, AExp: Integer; AFindSibling: TGetLineAddrFindSibling; AMaxSiblingDistance: integer = 0);
+  published
+    procedure TestLineMapFsNone;
+    procedure TestLineMapFsBefore;
+    procedure TestLineMapFsNext;
+  end;
+
+implementation
+
+procedure TTestLineMap.InitMap(l: array of integer);
+var
+  i: Integer;
+begin
+  LMap := Default(TDWarfLineMap);
+  LMap.Init;
+  for i := 0 to Length(l) - 1 do
+    LMap.SetAddressForLine(l[i], l[i]);
+  LMap.Compress;
+end;
+
+procedure TTestLineMap.CheckNotFound(ASearch: Integer; AFindSibling: TGetLineAddrFindSibling;
+  AMaxSiblingDistance: integer);
+var
+  a: TDBGPtrArray;
+  r: Boolean;
+  fl: Integer;
+begin
+  fl := -1;
+  r := LMap.GetAddressesForLine(ASearch, a, False, AFindSibling, @fl, AMaxSiblingDistance);
+  AssertFalse('not found '+IntToStr(ASearch), r);
+end;
+
+procedure TTestLineMap.CheckFound(ASearch, AExp: Integer; AFindSibling: TGetLineAddrFindSibling;
+  AMaxSiblingDistance: integer);
+var
+  a: TDBGPtrArray;
+  r: Boolean;
+  fl: Integer;
+begin
+  fl := -1;
+  r := LMap.GetAddressesForLine(ASearch, a, False, AFindSibling, @fl, AMaxSiblingDistance);
+  AssertTrue('found '+IntToStr(ASearch), r);
+  AssertTrue('found (data) for '+IntToStr(ASearch), Length(a) = 1);
+  AssertEquals('found '+IntToStr(ASearch), AExp, fl);
+  AssertEquals('found (addr) '+IntToStr(ASearch), AExp, a[0]);
+end;
+
+procedure TTestLineMap.TestLineMapFsNone;
+begin
+  InitMap([10]);
+
+  CheckFound(10, 10, fsNone);
+  CheckNotFound( 9, fsNone);
+  CheckNotFound(11, fsNone);
+
+  InitMap([1000]);
+  CheckNotFound(1, fsNone);
+  CheckNotFound(99999, fsNone);
+
+
+  InitMap([10, 20]);
+
+  CheckFound(10, 10, fsNone);
+  CheckFound(20, 20, fsNone);
+  CheckNotFound( 9, fsNone);
+  CheckNotFound(19, fsNone);
+  CheckNotFound(21, fsNone);
+
+  InitMap([10, 2000]);
+
+  CheckFound(10, 10, fsNone);
+  CheckFound(2000, 2000, fsNone);
+  CheckNotFound( 9, fsNone);
+  CheckNotFound(1999, fsNone);
+  CheckNotFound(2001, fsNone);
+end;
+
+procedure TTestLineMap.TestLineMapFsBefore;
+begin
+  InitMap([10]);
+
+  CheckFound(10, 10, fsBefore);
+  CheckFound(11, 10, fsBefore);
+  CheckFound(19, 10, fsBefore);
+  CheckFound(19, 10, fsBefore, 9);
+  CheckNotFound(19,  fsBefore, 8);
+  CheckNotFound( 9,  fsBefore);
+
+  InitMap([910, 920]);
+
+  CheckFound(910, 910, fsBefore);
+  CheckFound(911, 910, fsBefore);
+  CheckFound(919, 910, fsBefore);
+  CheckFound(919, 910, fsBefore, 9);
+  CheckNotFound(919,  fsBefore, 8);
+
+  CheckFound(920, 920, fsBefore);
+  CheckFound(921, 920, fsBefore);
+  CheckFound(929, 920, fsBefore);
+  CheckFound(929, 920, fsBefore, 9);
+  CheckNotFound(929,  fsBefore, 8);
+
+  CheckFound(2920, 920, fsBefore);
+  CheckNotFound(909,  fsBefore);
+  CheckNotFound(9,  fsBefore);
+
+  InitMap([511]);
+  CheckFound(2920, 511, fsBefore);
+  InitMap([512]);
+  CheckFound(2920, 512, fsBefore);
+
+end;
+
+procedure TTestLineMap.TestLineMapFsNext;
+begin
+  InitMap([10]);
+
+  CheckFound(10, 10, fsNext);
+  CheckFound( 9, 10, fsNext);
+  CheckFound( 1, 10, fsNext);
+  CheckFound( 1, 10, fsNext, 9);
+  CheckNotFound(11,  fsNext, 8);
+  CheckNotFound(11,  fsNext);
+
+  InitMap([910, 920]);
+
+  CheckFound(910, 910, fsNext);
+  CheckFound(909, 910, fsNext);
+  CheckFound(901, 910, fsNext);
+  CheckFound(901, 910, fsNext, 9);
+  CheckNotFound(901,  fsNext, 8);
+
+  CheckFound(920, 920, fsNext);
+  CheckFound(919, 920, fsNext);
+  CheckFound(911, 920, fsNext);
+  CheckFound(911, 920, fsNext, 9);
+  CheckNotFound(918,  fsNext, 1);
+  CheckNotFound(911,  fsNext, 8);
+
+  CheckFound(1, 910, fsNext);
+
+  CheckNotFound(921,  fsNext);
+  CheckNotFound(1921,  fsNext);
+
+  InitMap([10, 2000]);
+  CheckFound(11, 2000, fsNext);
+  CheckFound(311, 2000, fsNext);
+  CheckNotFound(11,  fsNext, 500);
+
+  InitMap([255]);
+  CheckFound(11, 255, fsNext);
+  InitMap([256]);
+  CheckFound(11, 256, fsNext);
+end;
+
+
+initialization
+
+  RegisterTest(TTestLineMap);
+end.
+