diff --git a/src/interpreter.c b/src/interpreter.c
index 3c199c9..a4562fe 100644
--- a/src/interpreter.c
+++ b/src/interpreter.c
@@ -1900,11 +1900,11 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
                         runtimeError(ARG_TYPE_MISMATCH, "Expecting a Value", in, currentInstruction);
                     }
                     if (function->nativeFn) {
-                        if (function->args[i].type == ANY || in->args.args[i + 1].value.value.type != function->args[i].type) {
+                        if (function->args[i].type != ANY || in->args.args[i + 1].value.value.type != function->args[i].type) {
                             runtimeError(ARG_TYPE_MISMATCH, "Mismatched function argument types", in, currentInstruction);
                         }
                     } else {
-                        if (function->args[i].type == ANY || !checkFnTypes(&in->args.args[i + 1].value.value, &function->args[i])) {
+                        if (function->args[i].type != ANY || !checkFnTypes(&in->args.args[i + 1].value.value, &function->args[i])) {
                             runtimeError(ARG_TYPE_MISMATCH, "Mismatched function argument types", in, currentInstruction);
                         }
                     }
@@ -1922,7 +1922,7 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
                         }
                         return returnValue;
                     }
-                    if (returnValue.type == ANY || returnValue.type != function->returnType) {
+                    if (returnValue.type != ANY && returnValue.type != function->returnType) {
                          runtimeError(RETURN_TYPE_MISMATCH, "Unexpected return value type from native function", in, currentInstruction);
                     }
                     addVariable(scope->variables, in->args.args[in->args.length - 1].value.refName, returnValue);
@@ -1934,7 +1934,7 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
                     if (in->args.args[i + 1].type != VALUE) {
                         runtimeError(ARG_TYPE_MISMATCH, "Expecting a Value", in, currentInstruction);
                     }
-                    if (function->args[i].type == ANY || function->args[i].type == ANY || !checkFnTypes(&in->args.args[i + 1].value.value, &function->args[i])) {
+                    if (function->args[i].type != ANY || !checkFnTypes(&in->args.args[i + 1].value.value, &function->args[i])) {
                         runtimeError(ARG_TYPE_MISMATCH, "Mismatched function argument types", in, currentInstruction);
                     }
                     addVariable(newScope.variables, function->args[i].name, in->args.args[i + 1].value.value);
@@ -1945,7 +1945,7 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
                 if (returnValue.type == ERROR) {
                     return returnValue;
                 }
-                if (function->returnType == ANY || returnValue.type != function->returnType) {
+                if (function->returnType != ANY && returnValue.type != function->returnType) {
                     runtimeError(RETURN_TYPE_MISMATCH, "Unexpected return value type from function", in, currentInstruction);
                 }
 
@@ -2004,11 +2004,11 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
                         runtimeError(ARG_TYPE_MISMATCH, "Expecting a Value", in, currentInstruction);
                     }
                     if (function->nativeFn) {
-                        if (function->args[i].type == ANY || in->args.args[i + 2].value.value.type != function->args[i].type) {
+                        if (function->args[i].type != ANY || in->args.args[i + 2].value.value.type != function->args[i].type) {
                             runtimeError(ARG_TYPE_MISMATCH, "Mismatched function argument types", in, currentInstruction);
                         }
                     } else {
-                        if (function->args[i].type == ANY || !checkFnTypes(&in->args.args[i + 2].value.value, &function->args[i])) {
+                        if (function->args[i].type != ANY || !checkFnTypes(&in->args.args[i + 2].value.value, &function->args[i])) {
                             runtimeError(ARG_TYPE_MISMATCH, "Mismatched function argument types", in, currentInstruction);
                         }
                     }
@@ -2045,8 +2045,8 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
                         }
                         return returnValue;
                     }
-                    if (returnValue.type != function->returnType) {
-                         runtimeError(function->returnType == ANY || RETURN_TYPE_MISMATCH, "Unexpected return value type from native function", in, currentInstruction);
+                    if (function->returnType != ANY && returnValue.type != function->returnType) {
+                         runtimeError(RETURN_TYPE_MISMATCH, "Unexpected return value type from native function", in, currentInstruction);
                     }
                     addVariable(scope->variables, in->args.args[in->args.length - 1].value.refName, returnValue);
 
@@ -2063,7 +2063,7 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
                         runtimeError(ARG_TYPE_MISMATCH, "Expecting a Value", in, currentInstruction);
                     }
                     //if (in->args.args[i + 1].value.value.type != function->args[i].type) {
-                    if (function->args[i].type == ANY || !checkFnTypes(&in->args.args[i + 2].value.value, &function->args[i])) {
+                    if (function->args[i].type != ANY || !checkFnTypes(&in->args.args[i + 2].value.value, &function->args[i])) {
                         runtimeError(ARG_TYPE_MISMATCH, "Mismatched function argument types", in, currentInstruction);
                     }
                     addVariable(newScope.variables, function->args[i].name, in->args.args[i + 2].value.value);
@@ -2076,7 +2076,7 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
                 if (returnValue.type == ERROR) {
                     return returnValue;
                 }
-                if (function->returnType == ANY || returnValue.type != function->returnType) {
+                if (function->returnType != ANY && returnValue.type != function->returnType) {
                     runtimeError(RETURN_TYPE_MISMATCH, "Unexpected return value type from function", in, currentInstruction);
                 }
                 addVariable(scope->variables, in->args.args[in->args.length - 1].value.refName, returnValue);