diff --git a/toolchain/language_server/context.cpp b/toolchain/language_server/context.cpp
index e5ca11723396..8aaa4df65cba 100644
--- a/toolchain/language_server/context.cpp
+++ b/toolchain/language_server/context.cpp
@@ -77,8 +77,8 @@ class DiagnosticConsumer : public Diagnostics::Consumer {
   auto GetRange(const Diagnostics::Loc& loc) -> clang::clangd::Range {
     return {.start = {.line = loc.line_number - 1,
                       .character = loc.column_number - 1},
-            .end = {.line = loc.line_number,
-                    .character = loc.column_number + loc.length}};
+            .end = {.line = loc.line_number - 1,
+                    .character = loc.column_number + loc.length - 1}};
   }
 
   // Converts a diagnostic level to an LSP severity.
diff --git a/toolchain/language_server/testdata/text_document/diagnostics.carbon b/toolchain/language_server/testdata/text_document/diagnostics.carbon
index 1b0a8a218152..8fa351a29c71 100644
--- a/toolchain/language_server/testdata/text_document/diagnostics.carbon
+++ b/toolchain/language_server/testdata/text_document/diagnostics.carbon
@@ -48,8 +48,8 @@
 // CHECK:STDOUT:         "message": "opening symbol without a corresponding closing symbol",
 // CHECK:STDOUT:         "range": {
 // CHECK:STDOUT:           "end": {
-// CHECK:STDOUT:             "character": 2,
-// CHECK:STDOUT:             "line": 1
+// CHECK:STDOUT:             "character": 1,
+// CHECK:STDOUT:             "line": 0
 // CHECK:STDOUT:           },
 // CHECK:STDOUT:           "start": {
 // CHECK:STDOUT:             "character": 0,
@@ -63,8 +63,8 @@
 // CHECK:STDOUT:         "message": "unrecognized declaration introducer",
 // CHECK:STDOUT:         "range": {
 // CHECK:STDOUT:           "end": {
-// CHECK:STDOUT:             "character": 2,
-// CHECK:STDOUT:             "line": 1
+// CHECK:STDOUT:             "character": 1,
+// CHECK:STDOUT:             "line": 0
 // CHECK:STDOUT:           },
 // CHECK:STDOUT:           "start": {
 // CHECK:STDOUT:             "character": 0,
@@ -78,8 +78,8 @@
 // CHECK:STDOUT:         "message": "semantics TODO: `handle invalid parse trees in `check``",
 // CHECK:STDOUT:         "range": {
 // CHECK:STDOUT:           "end": {
-// CHECK:STDOUT:             "character": 2,
-// CHECK:STDOUT:             "line": 1
+// CHECK:STDOUT:             "character": 1,
+// CHECK:STDOUT:             "line": 0
 // CHECK:STDOUT:           },
 // CHECK:STDOUT:           "start": {
 // CHECK:STDOUT:             "character": 0,
@@ -104,8 +104,8 @@
 // CHECK:STDOUT:         "message": "no return expression should be provided in this context",
 // CHECK:STDOUT:         "range": {
 // CHECK:STDOUT:           "end": {
-// CHECK:STDOUT:             "character": 20,
-// CHECK:STDOUT:             "line": 1
+// CHECK:STDOUT:             "character": 19,
+// CHECK:STDOUT:             "line": 0
 // CHECK:STDOUT:           },
 // CHECK:STDOUT:           "start": {
 // CHECK:STDOUT:             "character": 9,
diff --git a/toolchain/language_server/testdata/text_document/open_with_cpp_nonexistent.carbon b/toolchain/language_server/testdata/text_document/open_with_cpp_nonexistent.carbon
index 1c166bde0ac2..5be1f27d396b 100644
--- a/toolchain/language_server/testdata/text_document/open_with_cpp_nonexistent.carbon
+++ b/toolchain/language_server/testdata/text_document/open_with_cpp_nonexistent.carbon
@@ -44,8 +44,8 @@
 // CHECK:STDOUT:         "message": "'nonexistent.h' file not found",
 // CHECK:STDOUT:         "range": {
 // CHECK:STDOUT:           "end": {
-// CHECK:STDOUT:             "character": 11,
-// CHECK:STDOUT:             "line": 1
+// CHECK:STDOUT:             "character": 10,
+// CHECK:STDOUT:             "line": 0
 // CHECK:STDOUT:           },
 // CHECK:STDOUT:           "start": {
 // CHECK:STDOUT:             "character": 9,