diff --git a/interpreter/CMakeLists.txt b/interpreter/CMakeLists.txt
index 6cd3449727470..e6512a888284c 100644
--- a/interpreter/CMakeLists.txt
+++ b/interpreter/CMakeLists.txt
@@ -209,6 +209,11 @@ if(builtin_llvm)
 
   set(LLVM_ENABLE_PROJECTS "clang" CACHE STRING "")
 
+  # Always build LLVM with C++17. It is not necessary to compile with the same
+  # C++ standard as the rest of ROOT and sometimes it doesn't even work.
+  set(_cxx_standard ${CMAKE_CXX_STANDARD})
+  set(CMAKE_CXX_STANDARD 17)
+
   #---Reduce log level to suppress STATUS messages from LLVM
   if(NOT DEFINED CMAKE_MESSAGE_LOG_LEVEL)
     set(CMAKE_MESSAGE_LOG_LEVEL "NOTICE")
@@ -226,6 +231,8 @@ if(builtin_llvm)
     unset(CMAKE_MESSAGE_LOG_LEVEL)
   endif()
 
+  set(CMAKE_CXX_STANDARD ${_cxx_standard})
+
   set(LLVM_INCLUDE_DIRS ${CMAKE_CURRENT_SOURCE_DIR}/llvm-project/llvm/include
     ${CMAKE_CURRENT_BINARY_DIR}/llvm-project/llvm/include
     CACHE STRING "LLVM include directories."
@@ -372,7 +379,14 @@ else()
     # Disable linking against shared LLVM
     set(LLVM_LINK_LLVM_DYLIB OFF)
 
+    # Always build LLVM with C++17. It is not necessary to compile with the same
+    # C++ standard as the rest of ROOT and sometimes it doesn't even work.
+    set(_cxx_standard ${CMAKE_CXX_STANDARD})
+    set(CMAKE_CXX_STANDARD 17)
+
     add_subdirectory(llvm-project/clang EXCLUDE_FROM_ALL)
+
+    set(CMAKE_CXX_STANDARD ${_cxx_standard})
   endif(builtin_clang)
 
   set( CLANG_BUILT_STANDALONE 1 )
diff --git a/interpreter/llvm-project/llvm-project.tag b/interpreter/llvm-project/llvm-project.tag
index eba6c9f06e1a6..13158746c5fa1 100644
--- a/interpreter/llvm-project/llvm-project.tag
+++ b/interpreter/llvm-project/llvm-project.tag
@@ -1 +1 @@
-ROOT-llvm18-20250225-01
+ROOT-llvm18-20250313-01
diff --git a/interpreter/llvm-project/llvm/include/llvm/Support/ScopedPrinter.h b/interpreter/llvm-project/llvm/include/llvm/Support/ScopedPrinter.h
index aaaed3f5ceac6..2f6fff6f76e94 100644
--- a/interpreter/llvm-project/llvm/include/llvm/Support/ScopedPrinter.h
+++ b/interpreter/llvm-project/llvm/include/llvm/Support/ScopedPrinter.h
@@ -539,7 +539,13 @@ ScopedPrinter::printHex<support::ulittle16_t>(StringRef Label,
   startLine() << Label << ": " << hex(Value) << "\n";
 }
 
-struct DelimitedScope;
+struct DelimitedScope {
+  DelimitedScope(ScopedPrinter &W) : W(&W) {}
+  DelimitedScope() : W(nullptr) {}
+  virtual ~DelimitedScope() = default;
+  virtual void setPrinter(ScopedPrinter &W) = 0;
+  ScopedPrinter *W;
+};
 
 class JSONScopedPrinter : public ScopedPrinter {
 private:
@@ -838,14 +844,6 @@ class JSONScopedPrinter : public ScopedPrinter {
   }
 };
 
-struct DelimitedScope {
-  DelimitedScope(ScopedPrinter &W) : W(&W) {}
-  DelimitedScope() : W(nullptr) {}
-  virtual ~DelimitedScope() = default;
-  virtual void setPrinter(ScopedPrinter &W) = 0;
-  ScopedPrinter *W;
-};
-
 struct DictScope : DelimitedScope {
   explicit DictScope() = default;
   explicit DictScope(ScopedPrinter &W) : DelimitedScope(W) { W.objectBegin(); }