diff --git a/tools/toolchains/arm.py b/tools/toolchains/arm.py
index 70ac556226..68a7eda0bf 100644
--- a/tools/toolchains/arm.py
+++ b/tools/toolchains/arm.py
@@ -41,7 +41,7 @@ class ARM(mbedToolchain):
     SUPPORTED_CORES = ["Cortex-M0", "Cortex-M0+", "Cortex-M3", "Cortex-M4",
                        "Cortex-M4F", "Cortex-M7", "Cortex-M7F", "Cortex-M7FD", "Cortex-A9"]
     ARMCC_RANGE = (LooseVersion("5.06"), LooseVersion("5.07"))
-    ARMCC_VERSION_RE = re.compile("Component: ARM Compiler (\d+\.\d+)")
+    ARMCC_VERSION_RE = re.compile(b"Component: ARM Compiler (\d+\.\d+)")
 
     @staticmethod
     def check_executable():
@@ -99,7 +99,7 @@ class ARM(mbedToolchain):
         msg = None
         min_ver, max_ver = self.ARMCC_RANGE
         match = self.ARMCC_VERSION_RE.search(stdout)
-        found_version = LooseVersion(match.group(1)) if match else None
+        found_version = LooseVersion(match.group(1).decode("utf-8")) if match else None
         min_ver, max_ver = self.ARMCC_RANGE
         if found_version and (found_version < min_ver or found_version >= max_ver):
             msg = ("Compiler version mismatch: Have {}; "
diff --git a/tools/toolchains/gcc.py b/tools/toolchains/gcc.py
index 9387917bce..9a2a67c20b 100644
--- a/tools/toolchains/gcc.py
+++ b/tools/toolchains/gcc.py
@@ -31,7 +31,7 @@ class GCC(mbedToolchain):
     DIAGNOSTIC_PATTERN = re.compile('((?P<file>[^:]+):(?P<line>\d+):)(?P<col>\d+):? (?P<severity>warning|[eE]rror|fatal error): (?P<message>.+)')
 
     GCC_RANGE = (LooseVersion("6.0.0"), LooseVersion("7.0.0"))
-    GCC_VERSION_RE = re.compile("\d+\.\d+\.\d+")
+    GCC_VERSION_RE = re.compile(b"\d+\.\d+\.\d+")
 
     def __init__(self, target,  notify=None, macros=None, build_profile=None,
                  build_dir=None):
@@ -116,7 +116,7 @@ class GCC(mbedToolchain):
         stdout, _, retcode = run_cmd([self.cc[0], "--version"], redirect=True)
         msg = None
         match = self.GCC_VERSION_RE.search(stdout)
-        found_version = LooseVersion(match.group(0)) if match else None
+        found_version = LooseVersion(match.group(0).decode('utf-8')) if match else None
         min_ver, max_ver = self.GCC_RANGE
         if found_version and (found_version < min_ver or found_version >= max_ver):
             msg = ("Compiler version mismatch: Have {}; "
diff --git a/tools/toolchains/iar.py b/tools/toolchains/iar.py
index 92d9af8262..bf3712a76b 100644
--- a/tools/toolchains/iar.py
+++ b/tools/toolchains/iar.py
@@ -30,7 +30,7 @@ class IAR(mbedToolchain):
 
     DIAGNOSTIC_PATTERN = re.compile('"(?P<file>[^"]+)",(?P<line>[\d]+)\s+(?P<severity>Warning|Error|Fatal error)(?P<message>.+)')
     INDEX_PATTERN  = re.compile('(?P<col>\s*)\^')
-    IAR_VERSION_RE = re.compile("IAR ANSI C/C\+\+ Compiler V(\d+\.\d+)")
+    IAR_VERSION_RE = re.compile(b"IAR ANSI C/C\+\+ Compiler V(\d+\.\d+)")
     IAR_VERSION = LooseVersion("7.80")
 
     @staticmethod
@@ -99,7 +99,7 @@ class IAR(mbedToolchain):
         stdout, _, retcode = run_cmd([self.cc[0], "--version"], redirect=True)
         msg = None
         match = self.IAR_VERSION_RE.search(stdout)
-        found_version = match.group(1) if match else None
+        found_version = match.group(1).decode("utf-8") if match else None
         if found_version and LooseVersion(found_version) != self.IAR_VERSION:
             msg = "Compiler version mismatch: Have {}; expected {}".format(
                 found_version, self.IAR_VERSION)