diff --git a/tools/export/iar.py b/tools/export/iar.py
index 16a626a9ba..4393867ed7 100644
--- a/tools/export/iar.py
+++ b/tools/export/iar.py
@@ -35,16 +35,19 @@ class IAREmbeddedWorkbench(Exporter):
 
     MBED_CONFIG_HEADER_SUPPORTED = True
 
-    # backward compatibility with our scripts
-    TARGETS = []
-    for target in TARGET_NAMES:
-        try:
-            if (ProGenDef('iar').is_supported(str(TARGET_MAP[target])) or
-                ProGenDef('iar').is_supported(TARGET_MAP[target].progen['target'])):
-                TARGETS.append(target)
-        except AttributeError:
-            # target is not supported yet
-            continue
+    @property
+    def TARGETS(self):
+        if not hasattr(self, "_targets_supported"):
+            self._targets_supported = []
+            for target in TARGET_NAMES:
+                try:
+                    if (ProGenDef('iar').is_supported(str(TARGET_MAP[target])) or
+                        ProGenDef('iar').is_supported(TARGET_MAP[target].progen['target'])):
+                        self._targets_supported.append(target)
+                except AttributeError:
+                    # target is not supported yet
+                    continue
+        return self._targets_supported
 
     def generate(self):
         """ Generates the project files """
diff --git a/tools/export/uvision4.py b/tools/export/uvision4.py
index 17c62f2903..a4f684e832 100644
--- a/tools/export/uvision4.py
+++ b/tools/export/uvision4.py
@@ -36,16 +36,19 @@ class Uvision4(Exporter):
 
     MBED_CONFIG_HEADER_SUPPORTED = True
 
-    # backward compatibility with our scripts
-    TARGETS = []
-    for target in TARGET_NAMES:
-        try:
-            if (ProGenDef('uvision').is_supported(str(TARGET_MAP[target])) or
-                ProGenDef('uvision').is_supported(TARGET_MAP[target].progen['target'])):
-                TARGETS.append(target)
-        except AttributeError:
-            # target is not supported yet
-            continue
+    @property
+    def TARGETS(self):
+        if not hasattr(self, "_targets_supported"):
+            self._targets_supported = []
+            for target in TARGET_NAMES:
+                try:
+                    if (ProGenDef('uvision').is_supported(str(TARGET_MAP[target])) or
+                        ProGenDef('uvision').is_supported(TARGET_MAP[target].progen['target'])):
+                        self._targets_supported.append(target)
+                except AttributeError:
+                    # target is not supported yet
+                    continue
+        return self._targets_supported
 
     def get_toolchain(self):
         return TARGET_MAP[self.target].default_toolchain
diff --git a/tools/export/uvision5.py b/tools/export/uvision5.py
index 50ebf91906..3be797f0e3 100644
--- a/tools/export/uvision5.py
+++ b/tools/export/uvision5.py
@@ -37,15 +37,22 @@ class Uvision5(Exporter):
     MBED_CONFIG_HEADER_SUPPORTED = True
 
     # backward compatibility with our scripts
-    TARGETS = []
-    for target in TARGET_NAMES:
-        try:
-            if (ProGenDef('uvision5').is_supported(str(TARGET_MAP[target])) or
-                ProGenDef('uvision5').is_supported(TARGET_MAP[target].progen['target'])):
-                TARGETS.append(target)
-        except AttributeError:
-            # target is not supported yet
-            continue
+    def __init__(self):
+        self._targets = []
+
+    @property
+    def TARGETS(self):
+        if not hasattr(self, "_targets_supported"):
+            self._targets_supported = []
+            for target in TARGET_NAMES:
+                try:
+                    if (ProGenDef('uvision5').is_supported(str(TARGET_MAP[target])) or
+                        ProGenDef('uvision5').is_supported(TARGET_MAP[target].progen['target'])):
+                        self._targets_supported.append(target)
+                except AttributeError:
+                    # target is not supported yet
+                    continue
+        return self._targets_supported
 
     def get_toolchain(self):
         return TARGET_MAP[self.target].default_toolchain