diff --git a/base/BUILD.gn b/base/BUILD.gn
index 509aa373690d..020275b7aa05 100644
--- a/base/BUILD.gn
+++ b/base/BUILD.gn
@@ -1582,7 +1582,7 @@ component("base") {
     # TODO(b/206642994): see if we can remove this condition. It's added for now
     # because linking atomic leads to linker errors for evergreen on arm-hardfp,
     # and it's apparently not really needed (i.e., we can build without it).
-    if (!is_starboard || !sb_is_modular) {
+    if (!is_starboard || !(is_modular_toolchain && current_toolchain == cobalt_toolchain)) {
       libs += [ "atomic" ]
     }
   }
diff --git a/build/toolchain/gcc_toolchain.gni b/build/toolchain/gcc_toolchain.gni
index 1c1b364b1ec2..a4377d3b05a2 100644
--- a/build/toolchain/gcc_toolchain.gni
+++ b/build/toolchain/gcc_toolchain.gni
@@ -391,7 +391,7 @@ template("gcc_toolchain") {
       # TODO(b/206642994): see if we can remove this condition. It's needed for
       # now to add cflags for evergreen platforms but we haven't yet decided
       # whether cflags should be added here for all platforms.
-      if (!is_starboard_toolchain && is_starboard && sb_is_modular) {
+      if (!is_starboard_toolchain && is_starboard && is_modular_toolchain) {
         command = "$asm -MMD -MF $depfile ${rebuild_string}{{defines}} {{include_dirs}} {{cflags}} {{asmflags}}${extra_asmflags} -c {{source}} -o {{output}}"
       } else {
         command = "$asm -MMD -MF $depfile ${rebuild_string}{{defines}} {{include_dirs}} {{asmflags}}${extra_asmflags} -c {{source}} -o {{output}}"
diff --git a/cobalt/BUILD.gn b/cobalt/BUILD.gn
index 8fea180c0c24..74bcee3040f3 100644
--- a/cobalt/BUILD.gn
+++ b/cobalt/BUILD.gn
@@ -66,7 +66,7 @@ group("default") {
     "//third_party/brotli:dec_no_dictionary_data",
   ]
 
-  if (sb_is_modular) {
+  if (is_modular_toolchain && current_toolchain == cobalt_toolchain) {
     deps += [ "//base/util/values:values_util" ]
     if (sb_is_evergreen) {
       deps += [
diff --git a/cobalt/media/sandbox/BUILD.gn b/cobalt/media/sandbox/BUILD.gn
index 19be83551b45..8c39b5f2255b 100644
--- a/cobalt/media/sandbox/BUILD.gn
+++ b/cobalt/media/sandbox/BUILD.gn
@@ -58,7 +58,7 @@ target(final_executable_type, "web_media_player_sandbox") {
     "//url",
   ]
 
-  if (!sb_is_modular) {
+  if (!(is_modular_toolchain && current_toolchain == cobalt_toolchain)) {
     deps += cobalt_platform_dependencies
   }
 }
diff --git a/cobalt/network/BUILD.gn b/cobalt/network/BUILD.gn
index 1a4fd75969b0..a401eef8629b 100644
--- a/cobalt/network/BUILD.gn
+++ b/cobalt/network/BUILD.gn
@@ -80,7 +80,7 @@ static_library("network") {
     defines = [ "ENABLE_NETWORK_LOGGING" ]
   }
 
-  if (!sb_is_modular) {
+  if (!(is_modular_toolchain && current_toolchain == cobalt_toolchain)) {
     deps += cobalt_platform_dependencies
   }
 }
diff --git a/starboard/BUILD.gn b/starboard/BUILD.gn
index c0a010de11e2..11835f4d7484 100644
--- a/starboard/BUILD.gn
+++ b/starboard/BUILD.gn
@@ -58,8 +58,6 @@ group("gn_all") {
   }
 
   if (is_modular_toolchain && is_cobalt_toolchain) {
-    assert(sb_is_modular,
-           "sb_is_modular should be set when building with cobalt_toolchain")
   }
 
   if (!sb_is_evergreen) {
@@ -89,7 +87,7 @@ group("starboard") {
     "//starboard/client_porting/eztime",
   ]
 
-  if (sb_is_modular) {
+  if (is_modular_toolchain && current_toolchain == cobalt_toolchain) {
     public_deps += [
       "//third_party/llvm-project/compiler-rt:compiler_rt",
       "//third_party/llvm-project/libcxx:cxx",
@@ -192,7 +190,7 @@ if (current_toolchain == starboard_toolchain) {
     } else {
       public_deps += [ "//third_party/crashpad/wrapper:wrapper_stub" ]
     }
-    if (!sb_is_modular) {
+    if (!(is_modular_toolchain && current_toolchain == cobalt_toolchain)) {
       public_deps += [ "//$starboard_path:starboard_platform" ]
     }
   }
diff --git a/starboard/build/config/BUILD.gn b/starboard/build/config/BUILD.gn
index a9653497f346..3b440b4beca6 100644
--- a/starboard/build/config/BUILD.gn
+++ b/starboard/build/config/BUILD.gn
@@ -103,7 +103,7 @@ config("target") {
       # This appears to cause errors when linking the code statically,
       # however.
       # For windows based platforms this flag causes a linker error while building with cobalt toolchain
-      if (!(host_os == "win" && sb_is_modular &&
+      if (!(host_os == "win" && is_modular_toolchain &&
             current_toolchain == cobalt_toolchain)) {
         cflags = [ "-fPIC" ]
       }
@@ -153,7 +153,7 @@ config("starboard") {
       defines += [ "SB_IS_LIBRARY=1" ]
     }
 
-    if (sb_is_modular) {
+    if (is_modular_toolchain) {
       defines += [ "SB_IS_MODULAR=1" ]
     }
 
@@ -229,7 +229,9 @@ config("warnings_as_errors") {
 # override flags specified in a platform's "platform_configuration" config,
 # which is where these particular flags would otherwise naturally fit.
 config("default_compiler_flags") {
-  if (is_starboardized_toolchain && sb_is_modular && target_cpu == "arm") {
+  if (is_starboardized_toolchain &&
+      (is_modular_toolchain && current_toolchain == cobalt_toolchain) &&
+      target_cpu == "arm") {
     cflags = [ "-mfpu=vfpv3" ]
     asmflags = cflags
   }
diff --git a/starboard/build/config/base_configuration.gni b/starboard/build/config/base_configuration.gni
index 3c60204516c2..8e19f4c331e6 100644
--- a/starboard/build/config/base_configuration.gni
+++ b/starboard/build/config/base_configuration.gni
@@ -44,9 +44,6 @@ declare_args() {
   # Directory path to static contents' data.
   sb_static_contents_output_data_dir = "$root_out_dir/content/data"
 
-  # Whether this is a modular build.
-  sb_is_modular = false
-
   # Whether this is an Evergreen build.
   sb_is_evergreen = false
 
diff --git a/starboard/evergreen/shared/platform_configuration/configuration.gni b/starboard/evergreen/shared/platform_configuration/configuration.gni
index c76baea77b99..5b6a1c4d2de1 100644
--- a/starboard/evergreen/shared/platform_configuration/configuration.gni
+++ b/starboard/evergreen/shared/platform_configuration/configuration.gni
@@ -14,7 +14,7 @@
 
 import("//starboard/build/config/base_configuration.gni")
 
-sb_is_modular = true
+is_modular_toolchain = true
 
 sb_is_evergreen = true
 
diff --git a/starboard/extension/BUILD.gn b/starboard/extension/BUILD.gn
index 5212664b2e01..54f57adb6667 100644
--- a/starboard/extension/BUILD.gn
+++ b/starboard/extension/BUILD.gn
@@ -26,7 +26,7 @@ target(gtest_target_type, "extension_test") {
     "//testing/gmock",
     "//testing/gtest",
   ]
-  if (sb_is_modular) {
+  if (is_modular_toolchain && current_toolchain == cobalt_toolchain) {
     deps += cobalt_platform_dependencies
   }
 }
diff --git a/starboard/linux/shared/platform_configuration/BUILD.gn b/starboard/linux/shared/platform_configuration/BUILD.gn
index dcdaa48c857e..9ad7abc48153 100644
--- a/starboard/linux/shared/platform_configuration/BUILD.gn
+++ b/starboard/linux/shared/platform_configuration/BUILD.gn
@@ -143,7 +143,7 @@ config("platform_configuration") {
     "rt",
   ]
 
-  if (!sb_is_modular) {
+  if (!(is_modular_toolchain && current_toolchain == cobalt_toolchain)) {
     ldflags += [ "-static-libstdc++" ]
   }
 
diff --git a/third_party/boringssl/BUILD.gn b/third_party/boringssl/BUILD.gn
index f90940c03088..edf9cdcd6741 100644
--- a/third_party/boringssl/BUILD.gn
+++ b/third_party/boringssl/BUILD.gn
@@ -102,7 +102,7 @@ static_library("crypto") {
     configs -= [ "//starboard/build/config:size" ]
     configs += [ "//starboard/build/config:speed" ]
 
-    if (sb_is_modular) {
+    if (is_modular_toolchain && current_toolchain == cobalt_toolchain) {
       calling_convention = sabi_variables.calling_convention
       if ((calling_convention != "aarch64" && calling_convention != "eabi" &&
            calling_convention != "sysv" && calling_convention != "windows") ||
diff --git a/third_party/libjpeg-turbo/BUILD.gn b/third_party/libjpeg-turbo/BUILD.gn
index 43731152d8f5..e2ad5e06a89b 100644
--- a/third_party/libjpeg-turbo/BUILD.gn
+++ b/third_party/libjpeg-turbo/BUILD.gn
@@ -145,9 +145,9 @@ if (nasm_exists && (current_cpu == "x86" || current_cpu == "x64")) {
 }
 
 # TODO(b/206642994): look into whether we should condition on the
-# floating_point_fpu SABI variable, rather than sb_is_modular, here as we did
+# floating_point_fpu SABI variable, rather than (is_modular_toolchain && current_toolchain == cobalt_toolchain), here as we did
 # in third_party/libjpeg-turbo/libjpeg.gyp.
-if (is_starboard && sb_is_modular && current_cpu == "arm" && arm_use_neon) {
+if (is_starboard && (is_modular_toolchain && current_toolchain == cobalt_toolchain) && current_cpu == "arm" && arm_use_neon) {
   config("simd_arm_config") {
     cflags = [ "-mfpu=neon" ]
   }
@@ -205,7 +205,7 @@ static_library("simd") {
     }
     configs += [ "//build/config/compiler:optimize_speed" ]
 
-    if (is_starboard && sb_is_modular && current_cpu == "arm") {
+    if (is_starboard && (is_modular_toolchain && current_toolchain == cobalt_toolchain) && current_cpu == "arm") {
       configs += [ ":simd_arm_config" ]
     }
   } else {
@@ -316,7 +316,7 @@ static_library("libjpeg") {
   # TODO(b/236258535): Enable neon instructions once the code is updated
   # to use SbCPUFeatures() at runtime.
   if ((is_msan && (current_cpu == "x86" || current_cpu == "x64")) ||
-      (is_starboard && sb_is_modular)) {
+      (is_starboard && (is_modular_toolchain && current_toolchain == cobalt_toolchain))) {
     sources += [ "jsimd_none.c" ]
   } else {
     public_deps += [ ":simd" ]
diff --git a/third_party/zlib/BUILD.gn b/third_party/zlib/BUILD.gn
index 83cb3275eadf..e6fba1709b25 100644
--- a/third_party/zlib/BUILD.gn
+++ b/third_party/zlib/BUILD.gn
@@ -23,9 +23,9 @@ if (current_cpu == "arm" || current_cpu == "arm64") {
 }
 
 # TODO(b/206642994): look into whether we should condition on the
-# floating_point_fpu SABI variable, rather than sb_is_modular, here as we did
+# floating_point_fpu SABI variable, rather than (is_modular_toolchain && current_toolchain == cobalt_toolchain), here as we did
 # in third_party/zlib/zlib.gyp.
-if (is_starboard && sb_is_modular && target_cpu == "arm" &&
+if (is_starboard && (is_modular_toolchain && current_toolchain == cobalt_toolchain) && target_cpu == "arm" &&
     use_arm_neon_optimizations) {
   config("zlib_neon_fpu_config") {
     cflags = [ "-mfpu=neon" ]
@@ -80,7 +80,7 @@ source_set("zlib_adler32_simd") {
     configs += [ "//starboard/build/config:speed" ]
   }
 
-  if (is_starboard && sb_is_modular && target_cpu == "arm" &&
+  if (is_starboard && (is_modular_toolchain && current_toolchain == cobalt_toolchain) && target_cpu == "arm" &&
       use_arm_neon_optimizations) {
     configs += [ ":zlib_neon_fpu_config" ]
   }
@@ -161,7 +161,7 @@ if (use_arm_neon_optimizations) {
       deps = [ "//starboard:starboard_headers_only" ]
     }
 
-    if (is_starboard && sb_is_modular && target_cpu == "arm" &&
+    if (is_starboard && (is_modular_toolchain && current_toolchain == cobalt_toolchain) && target_cpu == "arm" &&
         use_arm_neon_optimizations) {
       configs += [ ":zlib_neon_fpu_config" ]
     }
@@ -236,7 +236,7 @@ source_set("zlib_inflate_chunk_simd") {
     configs += [ "//starboard/build/config:speed" ]
   }
 
-  if (is_starboard && sb_is_modular && target_cpu == "arm" &&
+  if (is_starboard && (is_modular_toolchain && current_toolchain == cobalt_toolchain) && target_cpu == "arm" &&
       use_arm_neon_optimizations) {
     configs += [ ":zlib_neon_fpu_config" ]
   }