diff --git a/toolchain/lower/context.cpp b/toolchain/lower/context.cpp
index 4b01daa48251..db8b4a165f2d 100644
--- a/toolchain/lower/context.cpp
+++ b/toolchain/lower/context.cpp
@@ -5,6 +5,7 @@
 #include "toolchain/lower/context.h"
 
 #include "clang/Basic/SourceManager.h"
+#include "clang/CodeGen/ModuleBuilder.h"
 #include "common/check.h"
 #include "common/growing_range.h"
 #include "common/raw_string_ostream.h"
diff --git a/toolchain/lower/context.h b/toolchain/lower/context.h
index 74819ed6f8f5..6a61f04ac2b1 100644
--- a/toolchain/lower/context.h
+++ b/toolchain/lower/context.h
@@ -20,6 +20,10 @@
 #include "toolchain/sem_ir/ids.h"
 #include "toolchain/sem_ir/inst_namer.h"
 
+namespace clang {
+class CodeGenerator;
+}
+
 namespace Carbon::Lower {
 
 class FileContext;
diff --git a/toolchain/lower/file_context.h b/toolchain/lower/file_context.h
index e634901100fe..b135a2f517ff 100644
--- a/toolchain/lower/file_context.h
+++ b/toolchain/lower/file_context.h
@@ -5,8 +5,6 @@
 #ifndef CARBON_TOOLCHAIN_LOWER_FILE_CONTEXT_H_
 #define CARBON_TOOLCHAIN_LOWER_FILE_CONTEXT_H_
 
-#include "clang/CodeGen/ModuleBuilder.h"
-#include "clang/Lex/PreprocessorOptions.h"
 #include "toolchain/lower/context.h"
 #include "toolchain/lower/specific_coalescer.h"
 #include "toolchain/lower/type.h"
@@ -15,6 +13,11 @@
 #include "toolchain/sem_ir/ids.h"
 #include "toolchain/sem_ir/inst_namer.h"
 
+namespace clang {
+class CodeGenerator;
+class FunctionDecl;
+}  // namespace clang
+
 namespace Carbon::Lower {
 
 // Information about how a given function declaration is lowered.