diff --git a/CryptoPkg/Library/OpensslLib/OpensslLibAccel.inf b/CryptoPkg/Library/OpensslLib/OpensslLibAccel.inf
index 912fd07f09..dd07d0f722 100644
--- a/CryptoPkg/Library/OpensslLib/OpensslLibAccel.inf
+++ b/CryptoPkg/Library/OpensslLib/OpensslLibAccel.inf
@@ -2003,7 +2003,7 @@
   #
   GCC:*_*_IA32_CC_FLAGS    = -U_WIN32 -U_WIN64 $(OPENSSL_FLAGS) $(OPENSSL_FLAGS_IA32) -Wno-error=maybe-uninitialized -Wno-error=unused-but-set-variable
   GCC:*_*_X64_CC_FLAGS     = -U_WIN32 -U_WIN64 $(OPENSSL_FLAGS) $(OPENSSL_FLAGS_X64) -Wno-error=maybe-uninitialized -Wno-error=format -Wno-format -Wno-error=unused-but-set-variable -DNO_MSABI_VA_FUNCS
-  GCC:*_CLANGDWARF_*_CC_FLAGS = -std=c99 -Wno-error=uninitialized -Wno-error=incompatible-pointer-types -Wno-error=pointer-sign -Wno-error=implicit-function-declaration -Wno-error=ignored-pragma-optimize
+  GCC:*_CLANGDWARF_*_CC_FLAGS = -std=gnu99 -Wno-error=uninitialized -Wno-error=incompatible-pointer-types -Wno-error=pointer-sign -Wno-error=implicit-function-declaration -Wno-error=ignored-pragma-optimize
   GCC:*_CLANGPDB_*_CC_FLAGS = -std=c99 -Wno-error=uninitialized -Wno-error=incompatible-pointer-types -Wno-error=pointer-sign -Wno-error=implicit-function-declaration -Wno-error=ignored-pragma-optimize
   # Revisit after switching to 3.0 branch
   GCC:*_GCC5_*_CC_FLAGS    = -Wno-unused-but-set-variable
diff --git a/CryptoPkg/Library/OpensslLib/OpensslLibFullAccel.inf b/CryptoPkg/Library/OpensslLib/OpensslLibFullAccel.inf
index 8f8b94c3ac..b65ecf1e37 100644
--- a/CryptoPkg/Library/OpensslLib/OpensslLibFullAccel.inf
+++ b/CryptoPkg/Library/OpensslLib/OpensslLibFullAccel.inf
@@ -2155,7 +2155,7 @@
   #
   GCC:*_*_IA32_CC_FLAGS    = -U_WIN32 -U_WIN64 $(OPENSSL_FLAGS) $(OPENSSL_FLAGS_IA32) -Wno-error=maybe-uninitialized -Wno-error=unused-but-set-variable
   GCC:*_*_X64_CC_FLAGS     = -U_WIN32 -U_WIN64 $(OPENSSL_FLAGS) $(OPENSSL_FLAGS_X64) -Wno-error=maybe-uninitialized -Wno-error=format -Wno-format -Wno-error=unused-but-set-variable -DNO_MSABI_VA_FUNCS
-  GCC:*_CLANGDWARF_*_CC_FLAGS = -std=c99 -Wno-error=uninitialized -Wno-error=incompatible-pointer-types -Wno-error=pointer-sign -Wno-error=implicit-function-declaration -Wno-error=ignored-pragma-optimize
+  GCC:*_CLANGDWARF_*_CC_FLAGS = -std=gnu99 -Wno-error=uninitialized -Wno-error=incompatible-pointer-types -Wno-error=pointer-sign -Wno-error=implicit-function-declaration -Wno-error=ignored-pragma-optimize
   GCC:*_CLANGPDB_*_CC_FLAGS = -std=c99 -Wno-error=uninitialized -Wno-error=incompatible-pointer-types -Wno-error=pointer-sign -Wno-error=implicit-function-declaration -Wno-error=ignored-pragma-optimize
   # Revisit after switching to 3.0 branch
   GCC:*_GCC5_*_CC_FLAGS    = -Wno-unused-but-set-variable