diff --git a/lldb/source/Core/CMakeLists.txt b/lldb/source/Core/CMakeLists.txt
index a4057d11077f3..a9bd2c6f31e9f 100644
--- a/lldb/source/Core/CMakeLists.txt
+++ b/lldb/source/Core/CMakeLists.txt
@@ -90,6 +90,11 @@ add_lldb_library(lldbCore
     Demangle
   )
 
+# Necessary to ensure that the SWIFT_INLINE_NAMESPACE macro is defined for
+# swiftDemangling inclusions.
+target_compile_definitions(lldbCore PRIVATE
+  SWIFT_INLINE_NAMESPACE=compiler)
+
 add_dependencies(lldbCore
   LLDBCorePropertiesGen
   LLDBCorePropertiesEnumGen)
diff --git a/lldb/source/Plugins/ExpressionParser/Swift/CMakeLists.txt b/lldb/source/Plugins/ExpressionParser/Swift/CMakeLists.txt
index c3333faf6a7b8..cf4ba5f106776 100644
--- a/lldb/source/Plugins/ExpressionParser/Swift/CMakeLists.txt
+++ b/lldb/source/Plugins/ExpressionParser/Swift/CMakeLists.txt
@@ -43,3 +43,8 @@ add_lldb_library(lldbPluginExpressionParserSwift PLUGIN
     Support
     Core
   )
+
+# Necessary to ensure that the SWIFT_INLINE_NAMESPACE macro is defined for
+# swiftDemangling inclusions.
+target_compile_definitions(lldbPluginExpressionParserSwift PRIVATE
+  SWIFT_INLINE_NAMESPACE=compiler)
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/CMakeLists.txt b/lldb/source/Plugins/SymbolFile/DWARF/CMakeLists.txt
index 382cf7ff0f7d0..a2ffc1ac1827c 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/CMakeLists.txt
+++ b/lldb/source/Plugins/SymbolFile/DWARF/CMakeLists.txt
@@ -70,3 +70,8 @@ add_lldb_library(lldbPluginSymbolFileDWARF PLUGIN
 add_dependencies(lldbPluginSymbolFileDWARF
   LLDBPluginSymbolFileDWARFPropertiesGen
   LLDBPluginSymbolFileDWARFPropertiesEnumGen)
+
+# Necessary to ensure that the SWIFT_INLINE_NAMESPACE macro is defined for
+# swiftDemangling inclusions.
+target_compile_definitions(lldbPluginSymbolFileDWARF PRIVATE
+  SWIFT_INLINE_NAMESPACE=compiler)
diff --git a/lldb/source/Symbol/CMakeLists.txt b/lldb/source/Symbol/CMakeLists.txt
index 8d303e164868a..04939c786cfe5 100644
--- a/lldb/source/Symbol/CMakeLists.txt
+++ b/lldb/source/Symbol/CMakeLists.txt
@@ -75,3 +75,8 @@ add_lldb_library(lldbSymbol
 if(CMAKE_CXX_COMPILER_ID STREQUAL Clang AND NOT SWIFT_COMPILER_IS_MSVC_LIKE)
   target_compile_options(lldbSymbol PRIVATE -Wno-dollar-in-identifier-extension)
 endif()
+
+# Necessary to ensure that the SWIFT_INLINE_NAMESPACE macro is defined for
+# swiftDemangling inclusions.
+target_compile_definitions(lldbSymbol PRIVATE
+  SWIFT_INLINE_NAMESPACE=compiler)
diff --git a/lldb/source/Target/CMakeLists.txt b/lldb/source/Target/CMakeLists.txt
index 5012ef1488b59..0d009c928add4 100644
--- a/lldb/source/Target/CMakeLists.txt
+++ b/lldb/source/Target/CMakeLists.txt
@@ -118,3 +118,8 @@ endif()
 add_dependencies(lldbTarget
   LLDBTargetPropertiesGen
   LLDBTargetPropertiesEnumGen)
+
+# Necessary to ensure that the SWIFT_INLINE_NAMESPACE macro is defined for
+# swiftDemangling inclusions.
+target_compile_definitions(lldbTarget PRIVATE
+  SWIFT_INLINE_NAMESPACE=compiler)