diff --git a/lldb/source/Interpreter/OptionValuePathMappings.cpp b/lldb/source/Interpreter/OptionValuePathMappings.cpp
--- a/lldb/source/Interpreter/OptionValuePathMappings.cpp
+++ b/lldb/source/Interpreter/OptionValuePathMappings.cpp
@@ -61,7 +61,7 @@
             count);
       } else {
         bool changed = false;
-        for (size_t i = 1; i < argc; i += 2, ++idx) {
+        for (size_t i = 1; i < argc; i += 2) {
           const char *orginal_path = args.GetArgumentAtIndex(i);
           const char *replace_path = args.GetArgumentAtIndex(i + 1);
           if (VerifyPathExists(replace_path)) {
@@ -70,9 +70,13 @@
             if (!m_path_mappings.Replace(a, b, idx, m_notify_changes))
               m_path_mappings.Append(a, b, m_notify_changes);
             changed = true;
+            idx++;
           } else {
+            std::string previousError =
+                error.Fail() ? std::string(error.AsCString()) + "\n" : "";
             error.SetErrorStringWithFormat(
-                "the replacement path doesn't exist: \"%s\"", replace_path);
+                "%sthe replacement path doesn't exist: \"%s\"",
+                previousError.c_str(), replace_path);
             break;
           }
         }
@@ -109,9 +113,11 @@
           m_value_was_set = true;
           changed = true;
         } else {
+          std::string previousError =
+              error.Fail() ? std::string(error.AsCString()) + "\n" : "";
           error.SetErrorStringWithFormat(
-              "the replacement path doesn't exist: \"%s\"", replace_path);
-          break;
+              "%sthe replacement path doesn't exist: \"%s\"",
+              previousError.c_str(), replace_path);
         }
       }
       if (changed)
@@ -135,7 +141,7 @@
         bool changed = false;
         if (op == eVarSetOperationInsertAfter)
           ++idx;
-        for (size_t i = 1; i < argc; i += 2, ++idx) {
+        for (size_t i = 1; i < argc; i += 2) {
           const char *orginal_path = args.GetArgumentAtIndex(i);
           const char *replace_path = args.GetArgumentAtIndex(i + 1);
           if (VerifyPathExists(replace_path)) {
@@ -143,9 +149,13 @@
             ConstString b(replace_path);
             m_path_mappings.Insert(a, b, idx, m_notify_changes);
             changed = true;
+            idx++;
           } else {
+            std::string previousError =
+                error.Fail() ? std::string(error.AsCString()) + "\n" : "";
             error.SetErrorStringWithFormat(
-                "the replacement path doesn't exist: \"%s\"", replace_path);
+                "%sthe replacement path doesn't exist: \"%s\"",
+                previousError.c_str(), replace_path);
             break;
           }
         }
diff --git a/lldb/test/API/functionalities/source-map/TestTargetSourceMap.py b/lldb/test/API/functionalities/source-map/TestTargetSourceMap.py
--- a/lldb/test/API/functionalities/source-map/TestTargetSourceMap.py
+++ b/lldb/test/API/functionalities/source-map/TestTargetSourceMap.py
@@ -1,6 +1,7 @@
 import lldb
 from lldbsuite.test.lldbtest import *
 from lldbsuite.test.decorators import *
+import os
 
 
 class TestTargetSourceMap(TestBase):
@@ -10,6 +11,21 @@
     @no_debug_info_test
     def test_source_map(self):
         """Test target.source-map' functionality."""
+
+        def assertBreakpointWithSourceMap(src_path):
+            # Set a breakpoint after we remap source and verify that it succeeds
+            bp = target.BreakpointCreateByLocation(src_path, 2)
+            self.assertEquals(bp.GetNumLocations(), 1,
+                            "make sure breakpoint was resolved with map")
+
+            # Now make sure that we can actually FIND the source file using this
+            # remapping:
+            retval = lldb.SBCommandReturnObject()
+            self.dbg.GetCommandInterpreter().HandleCommand("source list -f main.c -l 2", retval)
+            self.assertTrue(retval.Succeeded(), "source list didn't succeed.")
+            self.assertNotEqual(retval.GetOutput(), None, "We got no ouput from source list")
+            self.assertTrue("return" in retval.GetOutput(), "We didn't find the source file...")
+
         # Set the target soure map to map "./" to the current test directory
         src_dir = self.getSourceDir()
         src_path = os.path.join(src_dir, "main.c")
@@ -25,19 +41,68 @@
         bp = target.BreakpointCreateByLocation(src_path, 2)
         self.assertEquals(bp.GetNumLocations(), 0,
                         "make sure no breakpoints were resolved without map")
-        src_map_cmd = 'settings set target.source-map . "%s"' % (src_dir)
-        self.dbg.HandleCommand(src_map_cmd)
 
-        # Set a breakpoint after we remap source and verify that it succeeds
-        bp = target.BreakpointCreateByLocation(src_path, 2)
-        self.assertEquals(bp.GetNumLocations(), 1,
-                        "make sure breakpoint was resolved with map")
-
-        # Now make sure that we can actually FIND the source file using this
-        # remapping:
-        retval = lldb.SBCommandReturnObject()
-        self.dbg.GetCommandInterpreter().HandleCommand("source list -f main.c -l 2", retval)
-        self.assertTrue(retval.Succeeded(), "source list didn't succeed.")
-        self.assertNotEqual(retval.GetOutput(), None, "We got no ouput from source list")
-        self.assertTrue("return" in retval.GetOutput(), "We didn't find the source file...")
+        invalid_path = src_dir + "invalid_path"
+        invalid_path2 = src_dir + "invalid_path2"
+
+        # We make sure the error message contains all the invalid paths
+        self.expect(
+            'settings set target.source-map . "%s" . "%s" . "%s"' % (invalid_path, src_dir, invalid_path2),
+            substrs=[
+                'the replacement path doesn\'t exist: "%s"' % (invalid_path),
+                'the replacement path doesn\'t exist: "%s"' % (invalid_path2),
+            ],
+            error=True,
+        )
+        self.expect(
+            'settings show target.source-map',
+            substrs=['[0] "." -> "%s"' % (src_dir)],
+        )
+        assertBreakpointWithSourceMap(src_path)
+
+        # Index 0 is the valid mapping, and modifying it to an invalid one should have no effect
+        self.expect(
+            'settings replace target.source-map 0 . "%s"' % (invalid_path),
+            substrs=['error: the replacement path doesn\'t exist: "%s"' % (invalid_path)],
+            error=True,
+        )
+        self.expect(
+            'settings show target.source-map',
+            substrs=['[0] "." -> "%s"' % (src_dir)]
+        )
+        assertBreakpointWithSourceMap(src_path)
+
+        # Let's clear and add the mapping in with insert-after
+        self.runCmd('settings remove target.source-map 0')
+        self.expect(
+            'settings show target.source-map',
+            endstr="target.source-map (path-map) =\n",
+        )
         
+        # We add a valid but useless mapping so that we can use insert-after
+        another_valid_path = os.path.dirname(src_dir)
+        self.runCmd('settings set target.source-map . "%s"' % (another_valid_path))
+
+        self.expect(
+            'settings replace target.source-map 0 . "%s"' % (invalid_path),
+            substrs=['error: the replacement path doesn\'t exist: "%s"' % (invalid_path)],
+            error=True,
+        )
+        self.expect(
+            'settings show target.source-map',
+            substrs=['[0] "." -> "%s"' % (another_valid_path)]
+        )
+
+        # Let's clear and add the mapping in with append
+        self.expect('settings remove target.source-map 0')
+        self.expect(
+            'settings show target.source-map',
+            endstr="target.source-map (path-map) =\n",
+        )
+
+        self.expect(
+            'settings append target.source-map . "%s" . "%s"' % (invalid_path, src_dir),
+            substrs=['error: the replacement path doesn\'t exist: "%s"' % (invalid_path)],
+            error=True,
+        )
+        assertBreakpointWithSourceMap(src_path)