diff --git a/CMakeLists.txt b/CMakeLists.txt
index b9a0ce02d..3538b8041 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -8,8 +8,13 @@ option(ENABLE_PROGRAMS "Build mbed TLS programs." ON)
 
 option(UNSAFE_BUILD "Allow unsafe builds. These builds ARE NOT SECURE." OFF)
 
+string(REGEX MATCH "Clang" CMAKE_COMPILER_IS_CLANG "${CMAKE_C_COMPILER_ID}")
+string(REGEX MATCH "GNU" CMAKE_COMPILER_IS_GNU "${CMAKE_C_COMPILER_ID}")
+string(REGEX MATCH "IAR" CMAKE_COMPILER_IS_IAR "${CMAKE_C_COMPILER_ID}")
+string(REGEX MATCH "MSVC" CMAKE_COMPILER_IS_MSVC "${CMAKE_C_COMPILER_ID}")
+
 # the test suites currently have compile errors with MSVC
-if(MSVC)
+if(CMAKE_COMPILER_IS_MSVC)
     option(ENABLE_TESTING "Build mbed TLS tests." OFF)
 else()
     option(ENABLE_TESTING "Build mbed TLS tests." ON)
@@ -86,7 +91,7 @@ endfunction(link_to_source)
 
 string(REGEX MATCH "Clang" CMAKE_COMPILER_IS_CLANG "${CMAKE_C_COMPILER_ID}")
 
-if(CMAKE_COMPILER_IS_GNUCC)
+if(CMAKE_COMPILER_IS_GNU)
     # some warnings we want are not available with old GCC versions
     # note: starting with CMake 2.8 we could use CMAKE_C_COMPILER_VERSION
     execute_process(COMMAND ${CMAKE_C_COMPILER} -dumpversion
@@ -105,7 +110,7 @@ if(CMAKE_COMPILER_IS_GNUCC)
     set(CMAKE_C_FLAGS_ASANDBG     "-Werror -fsanitize=address -fno-common -O1 -g3 -fno-omit-frame-pointer -fno-optimize-sibling-calls ")
     set(CMAKE_C_FLAGS_CHECK       "-Werror -Os")
     set(CMAKE_C_FLAGS_CHECKFULL   "${CMAKE_C_FLAGS_CHECK} -Wcast-qual")
-endif(CMAKE_COMPILER_IS_GNUCC)
+endif(CMAKE_COMPILER_IS_GNU)
 
 if(CMAKE_COMPILER_IS_CLANG)
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -W -Wdeclaration-after-statement -Wwrite-strings -Wpointer-arith -Wimplicit-fallthrough -Wshadow")
@@ -119,16 +124,20 @@ if(CMAKE_COMPILER_IS_CLANG)
     set(CMAKE_C_FLAGS_CHECK       "-Werror -Os")
 endif(CMAKE_COMPILER_IS_CLANG)
 
-if(MSVC)
+if(CMAKE_COMPILER_IS_IAR)
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} --warn_about_c_style_casts --warnings_are_errors -Ohz")
+endif(CMAKE_COMPILER_IS_IAR)
+
+if(CMAKE_COMPILER_IS_MSVC)
     # Strictest warnings, and treat as errors
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /W3")
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /WX")
-endif(MSVC)
+endif(CMAKE_COMPILER_IS_MSVC)
 
 if(CMAKE_BUILD_TYPE STREQUAL "Coverage")
-    if(CMAKE_COMPILER_IS_GNUCC OR CMAKE_COMPILER_IS_CLANG)
+    if(CMAKE_COMPILER_IS_GNU OR CMAKE_COMPILER_IS_CLANG)
         set(CMAKE_SHARED_LINKER_FLAGS "--coverage")
-    endif(CMAKE_COMPILER_IS_GNUCC OR CMAKE_COMPILER_IS_CLANG)
+    endif(CMAKE_COMPILER_IS_GNU OR CMAKE_COMPILER_IS_CLANG)
 endif(CMAKE_BUILD_TYPE STREQUAL "Coverage")
 
 if(LIB_INSTALL_DIR)
diff --git a/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index 60b431a0f..2b5a61637 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -630,7 +630,13 @@ static inline int mbedtls_ssl_safer_memcmp( const void *a, const void *b, size_t
     volatile unsigned char diff = 0;
 
     for( i = 0; i < n; i++ )
-        diff |= A[i] ^ B[i];
+    {
+        /* Read volatile data in order before computing diff.
+         * This avoids IAR compiler warning:
+         * 'the order of volatile accesses is undefined ..' */
+        unsigned char x = A[i], y = B[i];
+        diff |= x ^ y;
+    }
 
     return( diff );
 }
diff --git a/library/asn1write.c b/library/asn1write.c
index 9555ecae8..c8db8beae 100644
--- a/library/asn1write.c
+++ b/library/asn1write.c
@@ -83,7 +83,9 @@ int mbedtls_asn1_write_len( unsigned char **p, unsigned char *start, size_t len
         return( 4 );
     }
 
+#if SIZE_MAX > 0xFFFFFFFF
     if( len <= 0xFFFFFFFF )
+#endif
     {
         if( *p - start < 5 )
             return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
@@ -96,7 +98,9 @@ int mbedtls_asn1_write_len( unsigned char **p, unsigned char *start, size_t len
         return( 5 );
     }
 
+#if SIZE_MAX > 0xFFFFFFFF
     return( MBEDTLS_ERR_ASN1_INVALID_LENGTH );
+#endif
 }
 
 int mbedtls_asn1_write_tag( unsigned char **p, unsigned char *start, unsigned char tag )
diff --git a/library/pkcs5.c b/library/pkcs5.c
index 440a174b5..f04f0ab25 100644
--- a/library/pkcs5.c
+++ b/library/pkcs5.c
@@ -249,8 +249,10 @@ int mbedtls_pkcs5_pbkdf2_hmac( mbedtls_md_context_t *ctx, const unsigned char *p
     memset( counter, 0, 4 );
     counter[3] = 1;
 
+#if UINT_MAX > 0xFFFFFFFF
     if( iteration_count > 0xFFFFFFFF )
         return( MBEDTLS_ERR_PKCS5_BAD_INPUT_DATA );
+#endif
 
     while( key_length )
     {