diff --git a/build/jam/BuildSetup b/build/jam/BuildSetup
index 0a97eb6c67..dee151c8ee 100644
--- a/build/jam/BuildSetup
+++ b/build/jam/BuildSetup
@@ -164,10 +164,14 @@ HAIKU_LINK = $(HAIKU_CC) ;
 HAIKU_LINKFLAGS = $(HAIKU_GCC_BASE_FLAGS) ;
 
 HAIKU_HDRS = [ FStandardHeaders ] ;
-HAIKU_CCFLAGS = $(HAIKU_GCC_BASE_FLAGS) -nostdinc ;
-HAIKU_C++FLAGS = $(HAIKU_GCC_BASE_FLAGS) -nostdinc ;
-HAIKU_KERNEL_CCFLAGS = $(HAIKU_GCC_BASE_FLAGS) ;
-HAIKU_KERNEL_C++FLAGS = $(HAIKU_GCC_BASE_FLAGS) ;
+
+HAIKU_CUSTOM_CCFLAGS = $(HAIKU_CCFLAGS) ;
+HAIKU_CUSTOM_C++FLAGS = $(HAIKU_C++FLAGS) ;
+
+HAIKU_CCFLAGS = $(HAIKU_GCC_BASE_FLAGS) $(HAIKU_CUSTOM_CCFLAGS) -nostdinc ;
+HAIKU_C++FLAGS = $(HAIKU_GCC_BASE_FLAGS) $(HAIKU_CUSTOM_C++FLAGS) -nostdinc ;
+HAIKU_KERNEL_CCFLAGS = $(HAIKU_GCC_BASE_FLAGS) $(HAIKU_CUSTOM_CCFLAGS) ;
+HAIKU_KERNEL_C++FLAGS = $(HAIKU_GCC_BASE_FLAGS) $(HAIKU_CUSTOM_C++FLAGS) ;
 HAIKU_DEFINES = __HAIKU__ ;
 HAIKU_NO_WERROR ?= 0 ;
 
@@ -361,10 +365,15 @@ switch $(HAIKU_ARCH) {
 	}
 	case x86 :
 	{
-		HAIKU_CCFLAGS += -march=pentium ;
-		HAIKU_C++FLAGS += -march=pentium ;
-		HAIKU_KERNEL_CCFLAGS += -march=pentium ;
-		HAIKU_KERNEL_C++FLAGS += -march=pentium ;
+		if $(HAIKU_CUSTOM_CCFLAGS) = '' {
+			HAIKU_CCFLAGS += -march=pentium ;
+			HAIKU_KERNEL_CCFLAGS += -march=pentium ;
+		}
+
+		if $(HAIKU_CUSTOM_C++FLAGS) = '' {
+			HAIKU_C++FLAGS += -march=pentium ;
+			HAIKU_KERNEL_C++FLAGS += -march=pentium ;
+		}
 
 		# Enable use of the gcc built-in atomic functions instead of atomic_*().
 		# The former are inlined and have thus less overhead. They are not