diff --git a/CryptoPkg/Library/BaseCryptLib/BaseCryptLib.inf b/CryptoPkg/Library/BaseCryptLib/BaseCryptLib.inf
index 38e25372b4..2a581ceac7 100644
--- a/CryptoPkg/Library/BaseCryptLib/BaseCryptLib.inf
+++ b/CryptoPkg/Library/BaseCryptLib/BaseCryptLib.inf
@@ -96,3 +96,5 @@
   # -JCryptoPkg/Include : To disable the use of the system includes provided by RVCT
   # --diag_remark=1     : Reduce severity of "#1-D: last line of file ends without a newline"
   RVCT:*_*_ARM_CC_FLAGS = -JCryptoPkg/Include --diag_remark=1
+
+  GCC:*_CLANG38_*_CC_FLAGS = -std=c99
diff --git a/CryptoPkg/Library/BaseCryptLib/PeiCryptLib.inf b/CryptoPkg/Library/BaseCryptLib/PeiCryptLib.inf
index 415dda3078..8fdc6920ec 100644
--- a/CryptoPkg/Library/BaseCryptLib/PeiCryptLib.inf
+++ b/CryptoPkg/Library/BaseCryptLib/PeiCryptLib.inf
@@ -93,3 +93,5 @@
   # -JCryptoPkg/Include : To disable the use of the system includes provided by RVCT
   # --diag_remark=1     : Reduce severity of "#1-D: last line of file ends without a newline"
   RVCT:*_*_ARM_CC_FLAGS = -JCryptoPkg/Include --diag_remark=1
+
+  GCC:*_CLANG38_*_CC_FLAGS = -std=c99
diff --git a/CryptoPkg/Library/BaseCryptLib/RuntimeCryptLib.inf b/CryptoPkg/Library/BaseCryptLib/RuntimeCryptLib.inf
index 5da5b31947..9d639fd01e 100644
--- a/CryptoPkg/Library/BaseCryptLib/RuntimeCryptLib.inf
+++ b/CryptoPkg/Library/BaseCryptLib/RuntimeCryptLib.inf
@@ -101,3 +101,5 @@
   # -JCryptoPkg/Include : To disable the use of the system includes provided by RVCT
   # --diag_remark=1     : Reduce severity of "#1-D: last line of file ends without a newline"
   RVCT:*_*_ARM_CC_FLAGS = -JCryptoPkg/Include --diag_remark=1
+
+  GCC:*_CLANG38_*_CC_FLAGS = -std=c99
diff --git a/CryptoPkg/Library/BaseCryptLib/SmmCryptLib.inf b/CryptoPkg/Library/BaseCryptLib/SmmCryptLib.inf
index f5dd213d1b..c9f4abb22a 100644
--- a/CryptoPkg/Library/BaseCryptLib/SmmCryptLib.inf
+++ b/CryptoPkg/Library/BaseCryptLib/SmmCryptLib.inf
@@ -98,3 +98,5 @@
   MSFT:*_*_*_CC_FLAGS = /wd4090
 
   XCODE:*_*_*_CC_FLAGS = -mmmx -msse
+
+  GCC:*_CLANG38_*_CC_FLAGS = -std=c99
diff --git a/CryptoPkg/Library/OpensslLib/OpensslLib.inf b/CryptoPkg/Library/OpensslLib/OpensslLib.inf
index f4d7772c06..ce04d44155 100644
--- a/CryptoPkg/Library/OpensslLib/OpensslLib.inf
+++ b/CryptoPkg/Library/OpensslLib/OpensslLib.inf
@@ -559,6 +559,7 @@
   GCC:*_*_X64_CC_FLAGS     = -U_WIN32 -U_WIN64 $(OPENSSL_FLAGS) -Wno-error=maybe-uninitialized -Wno-error=format -Wno-format -Wno-error=unused-but-set-variable -DNO_MSABI_VA_FUNCS
   GCC:*_*_ARM_CC_FLAGS     = $(OPENSSL_FLAGS) -Wno-error=maybe-uninitialized -Wno-error=unused-but-set-variable
   GCC:*_*_AARCH64_CC_FLAGS = $(OPENSSL_FLAGS) -Wno-error=maybe-uninitialized -Wno-format -Wno-error=unused-but-set-variable
+  GCC:*_CLANG38_*_CC_FLAGS = -std=c99 -Wno-error=uninitialized
 
   # suppress the following warnings in openssl so we don't break the build with warnings-as-errors:
   # 1295: Deprecated declaration <entity> - give arg types
diff --git a/CryptoPkg/Library/OpensslLib/OpensslLibCrypto.inf b/CryptoPkg/Library/OpensslLib/OpensslLibCrypto.inf
index fd12d112ed..35430e77d3 100644
--- a/CryptoPkg/Library/OpensslLib/OpensslLibCrypto.inf
+++ b/CryptoPkg/Library/OpensslLib/OpensslLibCrypto.inf
@@ -520,6 +520,7 @@
   GCC:*_*_X64_CC_FLAGS     = -U_WIN32 -U_WIN64 $(OPENSSL_FLAGS) -Wno-error=maybe-uninitialized -Wno-error=format -Wno-format -Wno-error=unused-but-set-variable -DNO_MSABI_VA_FUNCS
   GCC:*_*_ARM_CC_FLAGS     = $(OPENSSL_FLAGS) -Wno-error=maybe-uninitialized -Wno-error=unused-but-set-variable
   GCC:*_*_AARCH64_CC_FLAGS = $(OPENSSL_FLAGS) -Wno-error=maybe-uninitialized -Wno-format -Wno-error=unused-but-set-variable
+  GCC:*_CLANG38_*_CC_FLAGS = -std=c99 -Wno-error=uninitialized
 
   # suppress the following warnings in openssl so we don't break the build with warnings-as-errors:
   # 1295: Deprecated declaration <entity> - give arg types