diff --git a/config/companion_libs/cloog.in b/config/companion_libs/cloog.in
index dcac30d881..d6e129d296 100644
--- a/config/companion_libs/cloog.in
+++ b/config/companion_libs/cloog.in
@@ -1,31 +1,32 @@
 # CLooG options
 
+# CLooG 0.18.4 requires ISL 0.12 or newer
+# CLooG 0.18.1/0.18.0 frequires ISL 0.12 or older
 choice
     bool
     prompt "CLooG version"
 
-if ISL
-
 # Don't remove next line
 # CT_INSERT_VERSION_BELOW
 
 config CLOOG_V_0_18_4
     bool
     prompt "0.18.4"
+    depends on ISL_V_0_12_or_later
     select CLOOG_0_18_4_or_later
 
 config CLOOG_V_0_18_1
     bool
     prompt "0.18.1"
+    depends on !ISL_V_0_14_or_later
     select CLOOG_0_18_or_later
 
 config CLOOG_V_0_18_0
     bool
     prompt "0.18.0"
+    depends on !ISL_V_0_14_or_later
     select CLOOG_0_18_or_later
 
-endif # ISL
-
 endchoice
 
 config CLOOG_VERSION
diff --git a/config/companion_libs/isl.in b/config/companion_libs/isl.in
index 0584764345..eefbf34d88 100644
--- a/config/companion_libs/isl.in
+++ b/config/companion_libs/isl.in
@@ -1,5 +1,9 @@
 # ISL options
 
+# GCC 4.8 supports ISL 0.10 to 0.14
+# GCC 4.9 supports ISL 0.10 to 0.15
+# GCC 5   supports ISL 0.12 to 0.16
+# GCC 6   supports ISL 0.14 to 0.16
 choice
     bool
     prompt "ISL version"
@@ -9,30 +13,37 @@ choice
 config ISL_V_0_16_1
     bool
     prompt "0.16.1"
-    depends on CLOOG_0_18_4_or_later || CC_GCC_5_or_later
+    depends on CC_GCC_5_or_later
     select ISL_V_0_16_or_later
 
+config ISL_V_0_15
+    bool
+    prompt "0.15"
+    select ISL_V_0_15_or_later
+
 config ISL_V_0_14
     bool
     prompt "0.14"
-    depends on CLOOG_0_18_4_or_later || CC_GCC_5_or_later
     select ISL_V_0_14_or_later
 
 config ISL_V_0_12_2
     bool
     prompt "0.12.2"
-    depends on ! CLOOG_0_18_4_or_later || CC_GCC_5_or_later
+    depends on !CC_GCC_6_or_later
     select ISL_V_0_12_or_later
 
 config ISL_V_0_11_1
     bool
     prompt "0.11.1"
-    depends on ! CLOOG_0_18_4_or_later
-    depends on ! CC_GCC_5_or_later
+    depends on !CC_GCC_4_9_or_later
 
 endchoice
 
 config ISL_V_0_16_or_later
+    bool
+    select ISL_V_0_15_or_later
+
+config ISL_V_0_15_or_later
     bool
     select ISL_V_0_14_or_later
 
@@ -48,6 +59,7 @@ config ISL_VERSION
 # Don't remove next line
 # CT_INSERT_VERSION_STRING_BELOW
     default "0.16.1" if ISL_V_0_16_1
+    default "0.15" if ISL_V_0_15
     default "0.14" if ISL_V_0_14
     default "0.12.2" if ISL_V_0_12_2
     default "0.11.1" if ISL_V_0_11_1