diff --git a/prism/include/PrismHybridGlob.h b/prism/include/PrismHybridGlob.h
index 5ea94c3c..3d8e173c 100644
--- a/prism/include/PrismHybridGlob.h
+++ b/prism/include/PrismHybridGlob.h
@@ -83,7 +83,7 @@ extern double last_unif;
 
 // macros, function prototypes
 
-#define logtwo(X) log(X)/log(2)
+#define logtwo(X) log((double)X)/log(2.0)
 void PH_PrintToMainLog(JNIEnv *env, char *str, ...);
 void PH_PrintToTechLog(JNIEnv *env, char *str, ...);
 void PH_SetErrorMessage(char *str, ...);
diff --git a/prism/include/PrismSparseGlob.h b/prism/include/PrismSparseGlob.h
index 668f0f7c..d020182b 100644
--- a/prism/include/PrismSparseGlob.h
+++ b/prism/include/PrismSparseGlob.h
@@ -81,7 +81,7 @@ extern JNIEnv *export_env;
 
 // macros, function prototypes
 
-#define logtwo(X) log(X)/log(2)
+#define logtwo(X) log((double)X)/log(2.0)
 void PS_PrintToMainLog(JNIEnv *env, char *str, ...);
 void PS_PrintToTechLog(JNIEnv *env, char *str, ...);
 void PS_SetErrorMessage(char *str, ...);