diff --git a/src/main.cpp b/src/main.cpp
index d263c8a..7a396db 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -314,6 +314,9 @@ map<string, void*> loadedLibraries;
 // Map of function name to function pointer
 map<string, void*> externalFunctions;
 
+// Libraries currently imported
+vector<string> libraries;
+
 // Conversion functions
 GroundValue literalToGroundValue(const Literal& lit) {
     GroundValue gv;
@@ -1898,6 +1901,17 @@ Literal exec(vector<Instruction> in, bool executingFunction) {
                         error("First argument for use requires a string literal");
                     }
 
+                    string libName = get<string>(get<Literal>(l.args[0]).val);
+                    bool imported = false;
+                    for (string lib : libraries) {
+                        if (lib == libName) {
+                            imported = true;
+                            break;
+                        }
+                    }
+
+                    if (imported) break;
+
                     string groundLibsDir = getenv("GROUND_LIBS");
 
                     if (filesystem::exists(useName)) {
@@ -1917,6 +1931,7 @@ Literal exec(vector<Instruction> in, bool executingFunction) {
                     importing.push(get<string>(get<Literal>(l.args[0]).val));
                     Literal ret = exec(parser(lexer(in)), false);
                     importing.pop();
+                    libraries.push_back(libName);
                 }
                 break;
             case Instructions::Extern:
@@ -1936,6 +1951,16 @@ Literal exec(vector<Instruction> in, bool executingFunction) {
                         error("First argument for extern requires a string literal");
                     }
 
+                    bool imported = false;
+                    for (string lib : libraries) {
+                        if (lib == libName) {
+                            imported = true;
+                            break;
+                        }
+                    }
+
+                    if (imported) break;
+
                     // Add appropriate extension
                     string fullLibName = libName;
             #ifdef _WIN32